display Property
这是GNU Emacs Lisp参考文档的3.0版本,对应于Emacs23.3版本。
由张东亚汉化,汉化版本为0.9。
更新记录:
2011/06/22:启动第二章的翻译,待完成。 2011/07/02:完成第二章的翻译。
Copyright © 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “GNU General Public License,” with the Front-Cover texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.”
Appendices
--- 下列详细章节 --- ---------------------------------
这些章节是上面列出章节的子节,这里列出以便于你可以直接查阅。
惯例
描述信息格式
Lisp数据类型
编程类型
字符类型
Cons Cell和表类型
字符串类型
编辑类型
Numbers
Strings and Characters
Lists
Modifying Existing List Structure
Sequences, Arrays, and Vectors
Hash Tables
Symbols
Property Lists
Evaluation
Kinds of Forms
Control Structures
Nonlocal Exits
Errors
Variables
Scoping Rules for Variable Bindings
Buffer-Local Variables
Functions
Lambda Expressions
Macros
Common Problems Using Macros
Writing Customization Definitions
Customization Types
Loading
Byte Compilation
Advising Emacs Lisp Functions
Debugging Lisp Programs
The Lisp Debugger
Edebug
Breaks
The Outside Context
Edebug and Macros
Debugging Invalid Lisp Syntax
Reading and Printing Lisp Objects
Minibuffers
Completion
Command Loop
Defining Commands
Input Events
Reading Input
Keymaps
Menu Keymaps
Defining Menus
Major and Minor Modes
Hooks
Major Modes
Minor Modes
Mode Line Format
Font Lock Mode
Multiline Font Lock Constructs
Documentation
Files
Visiting Files
Information about Files
File Names
File Format Conversion
Backups and Auto-Saving
Backup Files
Buffers
Windows
Frames
Frame Parameters
Window Frame Parameters
Positions
Motion
Markers
Text
The Kill Ring
Indentation
Text Properties
Non-ASCII Characters
Coding Systems
Searching and Matching
Regular Expressions
Syntax of Regular Expressions
The Match Data
Syntax Tables
Syntax Descriptors
Parsing Expressions
Abbrevs and Abbrev Expansion
Processes
Receiving Output from Processes
Low-Level Network Access
Packing and Unpacking Byte Arrays
Emacs Display
The Echo Area
Reporting Warnings
Overlays
Faces
Fringes
The display Property
Images
Buttons
Abstract Display
Display Tables
Operating System Interface
Starting Up Emacs
Getting Out of Emacs
Terminal Input
Tips and Conventions
GNU Emacs Internals
Object Internals
GNU Emacs文本编辑器大部分由称为Emacs Lisp的编程语言写成,你可以用Emacs Lisp编写代码并将其作为扩展安装到Emacs上。然而,Emacs Lisp并不仅仅是一个“扩展性语言”,它是一个全功能的计算机编程语言,你可以象你用其他编程语言那样地使用它。
由于Emacs Lisp被设计成在编辑器内使用,它具有一些如扫描和分析文本以及处理文件、缓冲区、显示和子进程等独有的特性。Emacs Lisp和各种编辑功能紧密的结合在一起,因此,编辑命令可以做为函数在Lisp程序中被调用,而编辑器的定制参数就是普通的Lisp变量。
本文档将致力于对Emacs Lisp进行全面性的描述,对于初学者而言,如想阅读一些介绍性的文档,请参考由Free Software Foundation出版,Bob Chassell所写的An Introduction to Emacs Lisp Programming 。本书假定读者对于使用Emacs进行编辑有一定的了解,如需这方面的知识,可参考The GNU Emacs Manual文档。
总体而言,本书前面的章节描述了Emacs Lisp和其他编程语言相对应的一些特性,后面的章节则重点介绍Emacs Lisp独有的特性以及和编辑相关的特性。
本文档的版本为3.0,对应于Emacs版本23.3。
本文档几易其稿,但还不能说是完整无错。目前还有一些主题未被覆盖到,要么是因为它们相对次要(如大部分的独立mode),要么是因为还未来得及撰写, 正是因为我们暂时不能处理完它们,所以我们将这些内容刻意省略掉了。
本文档覆盖到的地方,基本上是正确无误的,因它对于它讲述的内容,从特定示例和描述性的文字到章节顺序等,欢迎读者指正。如果某些内容让你觉得疑惑, 或者需要通过查阅代码或者做实验来确定本文章未覆盖的内容,这说明本文档可能需要被修正,请知会我们。
在您使用本文档时,一时你发现错误,请您将其发送给我们;如果您发现一个简单且真实的例子来说明一个或一组函数,请尽量能将其写下来发给我们,请您 引用一下章节名、函数名或变量名,并说明一下您阅读文本的版本号。
请使用M-x report-emacs-bug提供宝贵建议和纠错。
Lisp(LISt Processing luanguage)于20世纪50年代在麻省理工学院(MIT)为研究人工智能而被首次开发出来。Lisp语言的强大能力使得它也 能应用于其他目的,如编写编辑命令。 此后的许多年里,许多不同风格的Lisp实现被开发出来,它们大多数受到了20世纪60年代在MIT的MAC项目编写的Maclisp的启发。最终这些实现者坐到 了一起,制定了Lisp系统的标准,称作Common Lisp。同时,MIT的Gerry Sussman和Guy Steele开发了一个简单但强大的Lisp方言(译注:这里沿用目前 翻译中通用的称法,Lisp的各种变种通常被称为方言),称作Scheme。
GNU Emacs Lisp受到的大部分的启发来自于Maclisp,小部分来自于Common Lisp。如果你熟悉Common Lisp,你将注意到很多相似点,然而,由于为 了降低GNU Emacs的内存需求,很多Common Lisp的特性被忽略或者简化;有时这些简化变动很大使得Common Lisp用户感到迷惑;我们将不时的指出GNU Emacs Lisp与Common Lisp不同,如果你不熟悉Common Lisp,不要紧,本文档是自包含的。 一部分Common Lisp的仿真可以通过cl库来得到,请查看相应内容see Overview。
Emacs Lisp并未受到任何来自Scheme的影响,但GNU项目也有一个称作Guile的Scheme实现,为了扩展性,我们新的GNU软件将都使用Guile开发(译注: 从这点也说明了Lisp的强大,可以用来实现各种软件,比如有名的Reddit网站早期就使用Common Lisp写成)。
如下章节解释了本文档中的一些记法惯例,你可以跳过本章节,后面可以跳回查阅。
纵贯本文档,”Lisp读取器“和"Lisp打印器"指那些Lisp用来将那些用文字表示的Lisp对象转为实际的Lisp对象以及实现相反功能的例程,细节请参考See 打印表示, 。你,正在阅读本文档的人,被认为是"程序员"并用"你"来着重强调。"用户"则指使用Lisp程序的人,包括你编写的Lisp程序。
Lisp示例代码被格式化成如(list 1 2 3)这样的形式,那些被描述的元语法变量(译注:所谓元语法变量,简单来说,就是为了说明语言本身所提出
一些变量,如foo、bar这些,关于详细的解释,请参考这个链接:元语法变量。
, 或者函数的参数,将被格式化成如first-number这样的形式。
nil和t1) 名为‘nil’的符号 2) 逻辑真值false 3) 空表(具有零个成员的表)
当它被用作变量时,nil的值总是nil。
对于Lisp读取器而言,‘()’和‘nil’是相等的,它们代表同样的Lisp对象,即符号nil,只所以采用不同的方式书写,主要是从读者的
角度考虑,在Lisp读取器读取了‘()’或‘nil’后,没有办法知道用户到底是用哪种形式编写的。
在本文档中,我们在需要强调空表时,将用()表示,而当我们强调逻辑真值false时,将用false表示,这也是一种好的Lisp编程惯例。
(cons 'foo ()) ; 强调空表 (setq foo-flag nil) ; 强调真值false
在需要真值的上下文中,所有非nil的值都被当做true 对待;然而推荐用t来表示真值中的true 。当你需要选择一个表示真值
true的值时,如果没有其他的考虑,建议使用t,符号t永远具有值t。
在Emacs Lisp中,nil和t是求值是自身的特殊符号,因此你可以不必引用(译注:引用是Emacs Lisp中的一个重要概念,对应于quote函数,
后面会讲到)它们而把它们当做常量使用,尝试改变它们的值将得到setting-constance错误,详情请参考See Constant Variables,。
当object是
t或nil中的任意一个时,返回非nil(译注,这里的非空表示不是nil,但并不代表返回t,比如求值(booleanp nil)会得到这样一个表(nil t),同样是真值true。
你可以进行求值操作的Lisp表达式称作型(译注:英文对应为form,因Lisp中最为常用的结果叫List,翻译过来都叫表,不易区分,因此这里翻译作型) ,对型进行求值总是得到一个结果,该结果是一个Lisp对象,在本文档的示例中,该过程用‘⇒’表示:
(car '(1 2))
⇒ 1
对上述过程你可以称为“car '(1 2))求值结果为1”。
当一个型是宏调用时,它将被展开为一个新的型,用于Lisp进行求值,我们用‘==>’表示展开结果,除外,我们也有可能将型最终的求值结果也表示出来:
(third '(a b c))
==> (car (cdr (cdr '(a b c))))
⇒ c
有时为了表示两个型产生相同的结果,我们用‘==’表示两个型严格相等:
(make-sparse-keymap) == (list 'keymap)
本文档的许多示例都会打印文本信息;如果你在Lisp的交互缓冲区(如‘*scratch*’)中执行示例代码时,打印出的文本信息将会被插入到该缓冲区中,
而如果你通过其他方式执行示例代码(如对eval-region函数进行求值),打印的文本信息将在回显区显示。
本文档的示例中使用‘-|’表示打印出的文本信息,而不考虑它们输出到什么地方,而型的求值结果(下面的示例中是bar)将和‘⇒’
跟在文本信息的下面一行:
(progn (prin1 'foo) (princ "\n") (prin1 'bar))
-| foo
-| bar
⇒ bar
一些示例将给出错误信息,这通常是在回显区显示一个错误信息,我们用‘error-->’开头的一行来显示错误信息,注意‘error-->’并不会显示在回显区中:
(+ 23 'x)
error--> Wrong type argument: number-or-marker-p, x
一些示例通过对文本的“前”、“后”版本的显示,演示如何对缓冲区的文本内容进行修改,这些示例将用两行中划线来标识缓冲区的文本内容, 除外,‘-!-’显示点的位置(当然,点的符号,并不是缓冲区文本的一部分,它标识了两个字符之间即点所处的位置)。
---------- Buffer: foo ----------
This is the -!-contents of foo.
---------- Buffer: foo ----------
(insert "changed ")
⇒ nil
---------- Buffer: foo ----------
This is the changed -!-contents of foo.
---------- Buffer: foo ----------
函数、变量、宏、命令、用户选项以及特殊型在本文档中用统一的形式进行描述。描述的第一行将是名称及其参数,如果可能的话,在第一行还会 显示其所属类别—函数、变量或其他任意形式。
函数、变量或者其他任何其他类别,将出现在行的开头。 描述信息紧跟在后面,有时候还会伴有示例。
在函数描述中,首先是函数的名称,跟着是参数名称列表,这些参数名称也将用在函数体中,代表参数的值。
在参数列表中,关键字&optional表示后面的参数(称为可选参数)可以被忽略,被忽略的参数的值默认为nil,注意在调用函数时不要加
&optional;而关键字&rest(后面必须只跟一个参数,也即说明&rest必须出现在最后一个参数的前面)表示在调用时,从&rest
所在位置开始,可以传递任意参数,这些任意参数将被合成在一个表中,作为单个参数(称为剩余参数)传递给函数,同样,在调用函数时不要加&rest。
下面是一个虚构的函数foo的描述:
函数
foo从integer2中减去integer1,然而将integers2表中的数值累加到的结果中,如果integer2未提供,将用默认值19替代它。(foo 1 5 3 9) ⇒ 16 (foo 5) ⇒ 14更直观的描述,
(foo w x y...) == (+ (- x w) y...)
任何参数,如果其命名包含类型名(如integer、integer1或buffer),通常表示该参数需要是该类型,而复数的命名(如buffers) 通常表示一个拥有该类型对象的表。参数指名的object可以是任意类型(详细的类型列表,请查阅See Lisp数据类型.),其他方式命名的参数(如new-file) 将在函数描述中进行特别讨论。在某些章节中,一些函数参数的共性描述,将在前面首先描述。
对于可选和剩余参数更为完整的描述,请参考See Lambda Expressions.。
命令、宏和特殊型的描述也采用上述形式,但字`Function'将被替换为对应的`Command'、`Macro'或`Special Form',命令是可以被交互式调用的 简单函数,宏处理参数的方式和函数不同(参数不进行求值),但仍用和函数相同的形式进行描述。
特殊型的描述用一种更为复杂的记法来指定可选和重复参数,这是因为它可以将参数列表用更为复杂的方式进行分解。‘[optional-arg]’ 说明那个optional-arg是可选的,而‘repeated-args...’代表零或多个参数,括号用来将若干个参数组成有层次的表结构。下面是一个 示例:
这个虚构的特殊型实现了一个循环,每次循环将执行body所表示的型,并自增变量var,在第一次循环中,变量的值为from的值,在后续的操作中 ,变量值每次自增(或者按inc的值指定的步长自增),循环将在变量var的值等于to的值时终止,下面是一个示例:
(count-loop (i 0 10) (prin1 i) (princ " ") (prin1 (aref vector i)) (terpri))如果from和to被忽略,在循环执行前,var将被绑定到nil,循环将在var的值非空时终止,下面是一个示例:
(count-loop (done) (if (pending) (fixit) (setq done t)))在这个特殊型中,变量from和to是可选的,但必须同时存在或同时忽略,在它们同时存在,inc成为可选参数,这些参数和var 一起,用括号形成一个表,用来和组成此特殊型的body区分开来。
变量指可以持有值的名字。尽管接近所有的变量都可以由用户设置,部分变量专门用来由用户改变,这些变量称为用户选项,常规变量和 用户选项使用和函数相同的描述,除了没有参数列表外。
下面是一个虚构的electric-future-map变量的描述:
variable.
此变量的值是一个被Electric Command Future Mode使用的完整键盘映射,这个映射中的函数允许你编辑你还未考虑执行的命令。
用户选项的描述与上面的变量描述相同,只不过`Variable'将被替换为`User Option'。
下面这些函数用于确定当前使用Emacs版本。
此函数返回描述当前使用的Emacs的版本的字符串,在bug报告中包含此字符串很有用。
(emacs-version) ⇒ "GNU Emacs 23.1 (i686-pc-linux-gnu, GTK+ Version 2.14.4) of 2009-06-01 on cyd.mit.edu"如果here非空,此函数将在点所处的前面插入版本字符串,并返回
nil。当此函数在交互模式下执行时, 它在回显区打印出相同的字符串信息,但却给出了一个前缀参数使得here非nil。
此变量的值是Emacs在本地站点上的编译时间,它是一个具有三个数值的表,象
current-time的值一样(see Time of Day)。emacs-build-time ⇒ (18846 52016 156039)
此变量的值是当前正在运行的Emacs的版本号,它是一个像
"23.1.1"这样的字符串,此字符串中的最后一个数字并不是Emacs的发布版本号, 在你在相同目录下编译Emacs时,它会自增,而具有四个数值的值,如"22.0.91.1",表示这是一个未发布的测试版本。
下面这两个变量从Emacs 19.23版本开始存在:
此节不再翻译,值得一提的是,在翻译本文档时,这里有一个中国人的名字,即Chong YiDong,当前这位仁兄正在美国研究物理,是目前的EMACS的总维护 者,对于牛人,我们除了敬仰外,还需要学习如何达到同样的高度:)。
本文档由如下作者写成:Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc. Additional sections were written by Miles Bader, Lars Brinkhoff, Chong Yidong, Kenichi Handa, Lute Kamstra, Juri Linkov, Glenn Morris, Thien-Thi Nguyen, Dan Nicolaescu, Martin Rudalics, Kim F. Storm, Luc Teirlinck, and Eli Zaretskii.
如下人员提供了纠错信息:Drew Adams, Juanma Barranquero, Karl Berry, Jim Blandy, Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, Jesper Harder, George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Stefan Monnier, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potorti, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Jason Rumney, Per Starbäck, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard Westman, Jean White, Eduard Wiebe, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn.
Lisp对象是由Lisp程序所使用或操作的一块数据,从Emacs Lisp的角度来讲,一个类型或数据类型是一些对象的集合。
每一个对象至少属于一个类型。具有相同类型的对象具有相似的数据结构,并经常在相同的上下文环境中被使用。类型可以重叠,对象可以属于两到多个类型, 因此,我们可以问对象是否属于一个特定类型,但不能说对象的类型是什么。
Emacs集成了一些基础的对象类型。这些类型是其他类型构造的基础,它们称为基础类型。每一个对象只能属于一个基础类型。这些类型包括整型、浮点型、 cons、符号、字符串、容器、哈希表、子函数、字节码函数以及一些特殊类型,如缓冲区等与编辑相关的类型。(See 编辑类型.)
每一个基础类型都有一相应的Lisp函数,用来检查对象是否属于该类型。
Lisp不同于其他语言,它的对象是类型自说明的,也即每个对象的原子类型隐含在对象自身里。例如,如果一个对象是容器类型,则不能将其做为数字进行处理,Lisp知道它属于容器,而非数字。
在大多数的语言里,程序员必须声明每个变量的类型,编译器知道其类型,该类型并不由数据表示。这种声明方式在Emacs Lisp中并不存在。一个Lisp变量可以具有任何类型的数据,并且记住你存储在 它里边的任何值及其类型等所有信息。(实际上,少数Emacs Lisp变量仅能存储特定类型的值,请参考See Variables with Restricted Values.)。
本章节将描述GNU Emacs Lisp中每个标准类型的作用、打印表示以及读取语法,如何使用这些类型,将在后面的章节进行详述。
对象的打印表示是指Lisp打印器(prin1函数的功能)对该对象的输出格式。每个数据类型都具有唯一的输出表示。对象的读取语法则指对该对象的Lisp读取器所接受的输入格式,
读取语法并不需要唯一,许多对象具有一个或多个读取语法(请参考See Read and Print.)。
大多情况下,一个对象的打印表示也是其读取语法。然而,某些类型并没有读取语法,这是因为在Lisp程序中并没有必要以常量的形式输入这些类型的对象。这些对象以哈希记法的形式打印,即由 ‘#<’、描述字符串(通常是对象名跟上类型名)以及一个终结的‘>’组成。例如:
(current-buffer)
⇒ #<buffer objects.texi>
哈希记法不能被读取,所以当Lisp读取器遇到一个‘#<’时将会产生一个invalid-read-syntax错误。
在其他语言里,表达式就是文本;没有其他形式。在Lisp中,一个表达式首先是一个Lisp对象,其次则是该对象的读取语法。通常不必做此区分,则你需要在脑中记住这一点,否则你将不时会觉得非常
迷惑。
当你以交互形式对表达式求值时,Lisp解释器将首先读取该表达式的文本表示,产生一个Lisp对象,然后对该对象进行求值(see Evaluation)。然而,求值和读取是两项活动,读取返回该文本
所表示的对象,该对象在后面可能会被求值,也可能不会。请参考See Input Functions.,了解read即读取对象的基本函数的描述。
注释是那些在程序中为了供人阅读程序的文本,对于程序本身没有任何影响。在Lisp中,不在一个字符串或字符常量中出现的一个分号(‘;’),表明注释开始直至行尾。Lisp读取器丢弃注释, 它们在Lisp系统中并不成为表示程序的Lisp对象的一部分。
‘#@count’构造器,跳过后继count个字符,适用于程序产生的包含二进制数据的注释。Emacs Lisp字节编译器在其输出文件中使用该构造器(参考see Byte Compilation), 但它并非为源文件所设计。
想要了解格式注释的惯例,请参考See Comment Tips.一节。
在Emacs Lisp中,有两类常见的类型,即用于Lisp编程的类型以及与编辑有关的类型,前者在许多Lisp实现中以各种形式存在,而后者则是Emacs Lisp特有的。
Emacs Lisp中的整数范围为−536870912至536870911(30位,例如:
-2**29
to
2**29 - 1)
在大数机器上(某些机器将提供更宽的范围),需要注意Emacs Lisp算术运算函数并不检查溢出,因此(1+ 536870911)就是−536870912。
整数的读取语法由一系列十进制的数字加上开始的可选符号再加上可选的结束的数点组成。Lisp解释器产生的打印表示,并不会加上前置的‘+’或后置的‘.’。
-1 ; 整数-1。 1 ; 整数1。 1. ; 同样是整数1。 +1 ; 同样是整数1。 1073741825 ; 在30位实现时,同样是整数1,译注:此处错误,与下段说明也矛盾,不是1,而是浮点数1073741825.0
有个特例则是,如果由一串数字表示的整数太大或者大小,不能成为有效的整数型对象时,Lisp读取器将以浮点数据读取(请参考see 浮点类型)。比如在大多数
机器上,536870912都将被读取成浮点数536870912.0。
更详细的信息,请参考See Numbers.一节。
浮点数是科学计数法的计算机记法,你可以将浮点数理解为分数加上10的幂值。有效位精度以及指数范围与机器相关;Emacs使用C语言的double类型来存储浮
点数值,其内部采用2的幂值而非10的幂值。
浮点数的打印表示可以是一个数点(至少有一个数字跟在其后)、一个指数、或者两个都包含。如‘1500.0’、‘15e2’、‘1.5e3’以及‘.15e4’ 是表示具有值1500的浮点数的五种表示方法,它们是相等的。
更详细的信息,请参考See Numbers.一节。
Emacs Lisp中的字符仅是一个整数而已,换句话说,字符由其字符编码表示。例如 ,字符A由整数65表示。
程序中时常会使用到单个字符,但更常见到的则是字符串,即由字符组成的序列。请参考See 字符串类型.。
字符串和缓冲区中的字符当前被限制在0到4194303,也即20位(请参考see Character Codes)。编码0到127即ASCII编码;其余的称为 非ASCII字符。代表键盘输入的字符,具有更宽的范围,它们用来编码Control、Meta、Shift等修饰键。
为了方便处理消息,Emacs Lisp有一些特殊函数,用于对一些字符产生可读的文本描述。请参考See Describing Characters.。
由于字符实际上就是整数值,字符的打印语法就是一个十进制数值。这也是字符的读取语法之一,但在Lisp程序中用这种方式并不是清晰的编程方式。你应当总是 使用Emacs Lisp提供的字符的特殊读取语法,这些语法用以问号开头。
字母型字符的通常读取语法是在字母前边前上问号,因此,‘?A’表示字符A,‘?B’表示字符B,‘?a’则表示字符a。
示例:
?Q ⇒ 81 ?q ⇒ 113
你可以使用相同的语法来表示标点字符,但通常在该字符前再加上一个‘\’更好一些,以便使Emacs编辑Lisp代码的命令不致于迷惑。例如‘?\(’用于表示 左括号。如果字符是‘\’,你则必须再在前面添加一个‘\’来表示它:‘?\\’。
你可以用‘?\a’、‘?\b’、‘?\t’、‘?\n’、‘?\v’、‘?\f’、‘?\s’、‘?\r’、‘?\d’以及‘?\e’分别表示 Control-g、退格、制表、换行、垂直制表、换页、空格、回车、删除以及退出字符。(折线以及跟在其后的‘?\s’则具有不同的含义,它表示对此组合后面的字符进行“super” 修饰。)因此:
?\a ⇒ 7 ; control-g, C-g ?\b ⇒ 8 ; 退格, <BS>, C-h ?\t ⇒ 9 ; 制表, <TAB>, C-i ?\n ⇒ 10 ; 换行, C-j ?\v ⇒ 11 ; 垂直制表, C-k ?\f ⇒ 12 ; 换页, C-l ?\r ⇒ 13 ; 回车, <RET>, C-m ?\e ⇒ 27 ; 退出, <ESC>, C-[ ?\s ⇒ 32 ; 空格, <SPC> ?\\ ⇒ 92 ; 反斜钱, \ ?\d ⇒ 127 ; 删除, <DEL>
由反斜线开始的序列也被称为转义序列,由于反斜线扮演了“转义字符”的角色;此术语与<ESC>无关。‘\s’则用在字符常量, 在字符串常量中,则用来表示空格。
在不具有特殊转义的字符前插入反斜线是允许的,并且是无害的,因此,‘?\+’与‘?+’等价。通常对于大多数字符而言,没有必要增加反斜线,但是, 你需要在‘()\|;'`"#.,’前增加反斜线,以避免迷惑编辑Lisp代码的Emacs命令。你也可以在空白字符如空格、制表、换行以及换页符前插入反斜线,但是,最 好使用易读的转义序列,如‘\t’或‘\s’来替代实际的如制表、空格等空白字符。(如果你在空格前输入了反斜线,你应当在其后再增加一个空格,以使其 与后面的文本区分开。译注:这句话较为疑惑,实际上在字符串中插入反斜线+空格会当被忽略,如"\ bbb"与"bbb"的值相等)。
除针对特殊控制字符的特殊转义序列外,Emacs提供了针对于非ASCII文本字符的几类转义语法。
你可以通过字符的Unicode编码来指定它。?\unnnn代表映射到Unicode码点‘U+nnnn’的字符(按照惯例,Unicode码点以十六
进制数给出)。对于码点高于U+nnnn的字行,需要用稍微不同的语法,即\U00nnnnnn,它代表码点为‘U+nnnnnn’的
字符。Unicode标准只定义了最高为‘U+10ffff’的码点,所以如果你定义大于该码点的字符,Emacs将产生一个错误。
之所以采用这种奇怪和不便的语法,主要是是为了和其他语言兼容。与其他语言不同,Emacs只在字符串常量和字符串中支持此语法。
字符最常见的读取语法用10进制或16进制字符码表示。采用10进制时,采用问号跟上一个反斜线加上10进制字符码(用3位10进制数字)的形式,因此‘?\101’表示字符
A,‘?\001’表示字符C-a,而?\002表示C-b。尽管这种语法可表示任意ASCII字符,但除非用精确的10进制数值表示
比ASCII表示重要时才用这种语法。
?\012 ⇒ 10 ?\n ⇒ 10 ?\C-j ⇒ 10
?\101 ⇒ 65 ?A ⇒ 65
采用16进制时,采用问号跟上一个反斜线加上‘x’再加上对应的16进制字符码的形式。你可以使用任意数量的16进制数,所以在这种方式下你可以表示任意字符。因此
‘?\x41’表示A,‘?\x1’表示C-a,而?\x8e0表示Latin-1字符
‘a’加上重音符。
控制字符可以采用另外一种读取语法,它由问号跟上一个反斜线加上脱字符再加上相应的非控制字字符(大小写皆可)。例如,‘?\^I’有‘?\^i’均是控制字符 C-i的有效读取语法,其相应的整数值是9。
除了‘^’外,你还可以使用‘C-’来替代,因此‘?\C-i’和‘?\^I’以及‘?\^i’等效。
?\^I ⇒ 9 ?\C-I ⇒ 9
在字符串和缓冲区中,只有在那些ASCII中存在的控制字符才允许出现。但考虑到键盘输入的需求,你可以用‘C-’将任意字符转换为控制字符,这些非 ASCII控制字符的编码除对应的非控制字符外,还包括被设置上的第 2**26 位,普通的终闻风而动无法产生非ASCII字符,但在X或者其他窗口系统下,你可以很容易的构造它们。
由于历史原因,Emacs将<DEL>字符与?控制字符(译注:即‘?\C-?’)视为等价字符。(译注:感兴趣的朋友不妨试下,在Emacs中,Ctl-?与DEL键的作用是相同的:))
?\^? ⇒ 127 ?\C-? ⇒ 127
因此,当前不可能表示在X窗口系统下的有效按键Control-?,由于大量的Lisp文件用这样的方式引用<DEL>,因此很难改变这个问题。
在表示文件或字符串的控制字符时,我们推荐用‘^’那样的语法,而在处理键盘输入的控制字符时,我们倾向于使用‘C-’语法,无论采用哪种语法,都不会对程序的意义产生任 何影响,但却可以指导用户更好的理解该程序。
meta字符指那些用<META>修饰的字符,用于表示这种字符的整数,其第 2**27 位被设置成上。我们使用高位来表示此修饰符以及其他修饰符,以便得到更宽的基本字符码。
在字符串里,当一个ASCII字符第 2**7 位被设置上时,表示它是一个meta字符,因此,可以被包含在字符串的meta字符具有128~255的范围,即普通ASCII字符的meta版本。 (请参考See Strings of Events.一节,以便了解字符串处理<META>的细节。)
meta字符的读取语法是‘\M-’。例如,‘?\M-A’代表M-A,你也可以用‘\M-’加上字符对应的十进制码,或者加上 ‘\C-’以及其他任意字符的读取语法。因此,你可以把M-A写做‘?\M-A’或者写做‘?\M-\101’,相似地,你可以把C-M-b 写做‘?\M-\C-b’或者写作‘?\C-\M-b’或者‘?\M-\002’。
图形化字符的大小写由其字符码表示,如ASCII通过‘a’和‘A’区分大小写,但ASCII却没有办法区分控制字符 的大小写。Emacs使用第 2**25 位来表示在键入控制字符时是否使用了shift键。仅在你使用X终端或者其他特殊终端时才可能做此区分,普通终端并不会上报这种区分。shift位的语法 为‘\S-’,因此‘?\C-\S-o’或‘?\C-\S-O’代表shifted-control-o字符。
X窗口系统定义了字符中可以出现的其他三个修饰位:hyper、super以及alt,对应的语法为 ‘\H-’、‘\s-’以及‘\A-’。(这些前缀需要区分大小写。)因此,‘?\H-\M-\A-x’表示Alt-Hyper-Meta-x。(注意 不跟‘-’的‘\s’代表空格字符。) 从数值上来说,alt相应的位为2**22,super相应的位为2**23,而hyper相应的位为2**24。
GNU Emacs Lisp中的符号是指具有名字的一个对象,符号名做为符号的打印表示。在常规Lisp应用中,借助于一个obarray(请参考see Creating Symbols) ,符号的名称是唯一的,也即没有两个同名的符号。
符号可以做为变量、函数名或者维护一个属性表,或者仅仅是为了和所有其他Lisp对象进行区分,以便可以可靠地识别出其在数据结构中的存在。在一个指定的上下文环境中, 通常符号只具有以上的一种用途, 但你可以独立地以任意以上方式使用该符号。
名字以冒号(‘:’)开始的符号称为关键字符号。这些符号将自动扮演常量的角色,并且通常只用于将未知符号与有限的替代符号进行比较。
符号名可以包含任意字符。大多数符号名由字母、数字以及标点符号‘-+=*/’组成。这些名字不需要特殊标记(译注:这里应当指用反斜线括起来),只要符号名看起来
不像数字,那么就足够使用了。(如果符号名看起来是数字,那就在它前面添加一个‘\’,强制使它被解释成符号)。字符‘_~!@$%^&:<>{}?’很少在符号名中被使用,
它们也不需要被特殊标记。所有此外其他可能在符号名中出现的字符,都需要用反斜线进行转义。与字符串中的反斜线应用相比,符号名中的反斜线只是简单的将反斜线后的单个字符括起
来,例如,在字符串中,‘\t’代表一个制表符,而符号名中的‘\t’,则仅仅是将字母‘t’括起来(译注:根据本段前面的描述,字母t是不需要转义的,因此符号名
中的\t与t实际上是相同的,可以通过symbol-name '\tb以及symbol-name 'tb对比看看。)。为了在符号名中引入制表符,你需要用反斜线加上一个真实的
制表符来表示,但却很少需要这样做。
Common Lisp注记: 在Common Lisp中,小写字符总是被转成大写,除非它们被精确的转义。在Emacs Lisp中,大小写字母是不同的。
以下是符号名的几个例子。注意第五个例子中的‘+’被转义,以避免该符号被解释成数字,这种方式在第四个例子中并不需要,这里因为该符号名并不能被当做数字解释。
foo ; 名为‘foo’的符号。 FOO ; 名为‘FOO’的符号, 与‘foo’不同。 1+ ; 名为‘1+’的符号。 ; (不是‘+1’, 它是一个数字)。 \+1 ; 名为‘+1’的符号。 ; (并不是一个非常可读的名字)。 \(*\ 1\ 2\) ; 名为‘(* 1 2)的符号’ (糟糕的名字)。 +-*/_~!@$%^&=:<>{} ; 名为‘+-*/_~!@$%^&=:<>{}的符号’。 ; 这些符号不需要转义。
通常Lisp读取器扣留所有符号(译注:英文名为intern,目前暂找不出更好的名字,在Emacs中,intern就是将符号插入obarray中,而避免intern 就是相当于让符号游离在obarray之外。)。你可以在符号名前添加‘#:’来避免扣留发生。
序列是一个代表有序元素集的对象。在Emacs Lisp中,有两类序列,即表和数组。因此,表对象或者数组对象都可以认为是序列。
数组可以继续被细分为字符串、容器、字符表以及布尔容器。容器可以存储任何类型的元素,但字符串必须存储字符,而布尔容器的元素则只能是t
或nil。字符表除了它被任意有效字符索引的特性外,很象容器。字符串里的字符们可以像缓冲区里的字符一样,具有文本属性。(请参考see Text Properties),
但容器即使其元素是字符,也并不支持文本属性。
表、字符串以及其他的数组类型是不同的,但它们却具有一些相似性。例如,都有一个长度l,并且其元素可以以0到l减一的的数值去索引。某些被称为
序列函数,可以接受各种序列。例如,函数elt可以通过指定一个索引获取序列中的一个元素。(请参考See Sequences Arrays Vectors.)
因为序列总是在读取时被创建,因此通常不可能将同一个序列读取两次,如果你对序列的读取语法读取了两次,你将得到两个具有相同内容的序列(译注:这句话强调的应当是
将产生两个相同内容但不同的序列对象),但有一个不同,空表()总是代表相同的对象,即nil。
cons cell是一个具有两个槽的对象,分别称为car槽和cdr槽。每个槽都可以持有或指向任意Lisp对象。我们也用 “这个cons cell的car”来指代该对象car槽持有的任意对象,对于cdr槽持有的对象相似,可做相似称呼。
C程序员注意:在Lisp中,我们并不区分“持有”一个值和“引用”该值,因为在Lisp中,指针是隐式的。
表是一系列的cons cell,依次通过cdr链接在一起,每个cons cell的cdr槽或者引用下一个cons cell,或者
引用空表。对于那些操作表的函数,空表实际上是符号nil。(请参考See Lists.)因为大部分cons cell都作为表的
一部分,因此短语表结构被用来指代任何由cons cell组成的结构(译注:这里隐含着半句话,即“以便用来和表做区分”)。
由于cons cell们对于表如此重要,我们也有这样一个说法,即“不是cons cell的对象”,这些对象被称为原子。
表的读取语法和打印表示是相等的,并且包含一个左括号,任意数量的元素以及一个右括号。以下是表的例子:
(A 2 "A") ; 具有三个元素的表。 () ; 没有元素的表(空表)。 nil ; 没有元素的表(空表)。 ("A ()") ; 具有一个元素的表,元素是:"A ()"。 (A ()) ; 具有两个元系的空表,元素是:A和空表。 (A nil) ; 同上。 ((A B C)) ; 具有一个元素的表,表的元素是 ; 一个具有三个元素的表。
在读取时,括号内的每个对象都变成表的一个元素。也就是说,cons cell由各个元素组成。car槽持有一个元素,其cdr引用
表中的下一个cons cell,该cons cell持有表的下一个元素。表中最后个cons cell的cdr被设置为nil。
car和cdr从Lisp的历史演变而来。原始的Lisp实现运行在一个IBM 704计算机上,该计算机被分为两部分,分别叫作“地址”部分和
“剩余”部分;car是用于取得寄存器地址部分对应内容的指令,而cdr则是用于取得寄存器剩余部分对应内容的指令。相比之下,“cons cells”用于命名
创建它的函数cons,即如其名所识,construction of cells。(译注:这句不翻译,否则不易理解cons cells的意义)
可以将cons cells画成盒子对,象多米诺一样的形式对表进行图解。(Lisp读取器不能读取这种描绘方式,不象文本记法,可以被人和计算机读取,盒式描绘方式不能被
计算机读取:))此图表示了一个具有三元素的表(rose violet buttercup)():
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
在此图解中,每个盒子代表一个可以持有或者引用任意Lisp对象的槽。每对盒子对代表一个cons cell,每个箭头代表对一个Lisp对象的引用,该对象可以是一个原子, 也可以是另一个cons cell。
在这个例子中,第一个盒子,持有着第一个cons cell的car部分,引用rose(一个符号)。第二个盒子,持有第一个cons cell的cdr,引用下
一个cons cell。第二个cons cell的car是violet,它的cdr是第三个cons cell。第三个即最后一个cons cell的cdr是nil。
下面是该表的另一个图解,(rose violet buttercup),用另外一个方式进行描绘。
--------------- ---------------- -------------------
| car | cdr | | car | cdr | | car | cdr |
| rose | o-------->| violet | o-------->| buttercup | nil |
| | | | | | | | |
--------------- ---------------- -------------------
没有元素的表称为空表;它等同于符号nil。换句话说,nil既是一个符号,又是一个表。
下面是表(A ()),或者等价的(A nil),由盒子和箭头描绘:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> A --> nil
下面是一个更为复杂的刻画,显示了一个三元素表((pine needles) oak maple),第一个元素是一个具有两个元素的表:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| --> oak --> maple
|
| --- --- --- ---
--> | | |--> | | |--> nil
--- --- --- ---
| |
| |
--> pine --> needles
上述表用第二种盒子记法如下:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| o | o------->| oak | o------->| maple | nil |
| | | | | | | | | |
-- | --------- -------------- --------------
|
|
| -------------- ----------------
| | car | cdr | | car | cdr |
------>| pine | o------->| needles | nil |
| | | | | |
-------------- ----------------
点对记法是用来显式表示car和cdr的常见语法。使用这种语法时,(a . b)表示car是对象a而cdr
是对象b的cons cell。由于cdr不一定需要是表,因此点对记法比表语法更为普遍。然而,在表语法可用时,如果使用点对记法,则显得较为笨拙。
在点对记法中,‘(1 2 3)’写作‘(1 . (2 . (3 . nil)))’。对于由nil终结的表,两种语法都可以使用,但表语法更为方便。当打印一
个表时,点对记法仅在cons cell的cdr不是一个表时使用。
下面是用盒子演示点对记法的一个例子。此例子显示点对(rose . violet):
--- ---
| | |--> violet
--- ---
|
|
--> rose
借助于非nil终结的cdr,你可以组合点对记法和表记法来方便表示一个cons cell链。你在表的最后一个元素后写下一个点,并跟跟上最后一个
cons cell的cdr。例如,(rose violet . buttercup)和(code . (violet . buttercup))相等,这个对象看起来是这样的:
--- --- --- ---
| | |--> | | |--> buttercup
--- --- --- ---
| |
| |
--> rose --> violet
语法(rose . violet . buttercup) 是无效的,这是因为它没有任何意义。如果非要说明其意义的话,可以说将buttercup放至
一个cons cell的cdr中,而该cons cell的cdr已经是violet了。(译注:这是由于(violet . buttercup)没有被括起来,
要好考体会一下上面对点对记法的描述。)
表(rose violet)和(rose . (violet)等价,它看起来是这个样子:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> rose --> violet
相似地,三元素表(rose violet buttercup)与(rose . (violet . buttercup)等价。
它看起来是这个样子:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
关联表或alist是一种特殊构造的表,其元素是cons cells。在每个元素里,car被当作一个关键字,而cdr则被 当作关联值。(在某些情况下,关联值存储在cdr的car中。)关联表通常用作栈,因为在关联表的前面添加或删除关联很简单。
例如:
(setq alist-of-colors
'((rose . red) (lily . white) (buttercup . yellow)))
设置变量alist-of-colors为一个具有三元素的关联表。在第一个元素中,rose是关键字,而red是关联值。
要进步请了解关联表以及操作它的函数,请参考See Association Lists.一节。要了解另外一类用于处理大量具有关键字的的查找 表,请参考See Hash Tables.一节。
数组由任意数量的槽组成,这此槽用于持有或引用其他Lisp对象,布局在连续的内存块中。访问数组的任意元素花费大约相同的时间。 相比下,访问表元素的时间则与元素在表中的位置成比例关系。(表靠后的元素访问起来要比表靠前的元素耗时长。)
Emacs定义了四类数组:字符串、容器、布尔容器以及字符表。
字符串是一个由字符构成的数组,而容器则是由任意Lisp对象构成的数组。布尔容器只可持有t或nil。这些数组长度可达
最大的整数值。而字符表则是由有效字符码索引的稀松数组,它可持有任意Lisp对象。
数组的第一个元素索引为0,第而个元素索引为1,依次类推。这称为自0开始的索引方式。例如,一个具有四元素的数组,其索引为 0、1、2、和3。数组最大的索引值为其长度减1。数组一旦被创建,其索引就固定了。
所有的Emacs Lisp数组都是一维的。(大部分其他语法都支持多维数组,但这并不必要,你可通过嵌套一维数组达到同样的效果)。每类 数组都具有其特有的读取语法,详见后续的章节。
数组类型是序列的子类,包含字符串类型、容器类型、布尔容器类型以及字符表类型。
字符串是由字符组成的数组。字符串在Emacs中有多种用途,正如在文本编辑器中的作用一样;例如,可以作为Lisp符号的名称, 作为给用消息,作为从缓冲区中读取的文本。在Lisp中的字符串是常量:对其求值得到相同的字符串。
关于操作字符串的函数,请参考See Strings and Characters.。
字符串的读取语法以双引号开始,加上任意数量的字符,再加上另一个双引号结束,如"like this"。要在字符串中引用一个双引号,
请在双引号前加上反斜线;因此"\""是一个仅由反斜线组成的字符串。相似地,你可以通过在反斜线前增加反斜线,以便在字符串引用包
含反斜线,如:"this \\ is a single embedded backslash"。
换行符对于字符串的读取语法而言并不特殊;你可以在两个反斜线之间插入换行符,它将成为字符串的一个字符,但被转义后的换行符,即 前面有一个‘\’的换行符,将不会成为字符串的一部分,即Lisp读取器将在读取字符串时忽略该换行符。相似地,一个转义后的空格‘\ ’ 也将被忽略。
"It is useful to include newlines
in documentation strings,
but the newline is \
ignored if escaped."
⇒ "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."
你可以在字符串常量中逐字地写下非ASCII国际化字符。在Emacs字符串(和缓冲区中),对于非ASCII字符, 有两种表示:单字节或多字符。如果字符串常量从多字节源中读取,如多字节缓冲区或多字节字符串,或一个可以以多字节方式 访问的文件,那么字符将以多字节字符地形式被读取,进而使得字符串成为多字节的。如果字符串常量从单字节源中读取,那么 字符将以单字节形式读取,进而使得字符串成为单字节的。
对于多字节非ASCII字符,你还可以用其字符编码表示它:使用一个十六进制转义,‘\xnnnnnnn’, 必要时可以用任意的数字。(多字节非ASCII字符的编码都大于256。)任意下一个字符如果其十六进制数字无效,将 使得停止读取字符串。如果下一个字符可以被解释成十六进制数字,写一个‘\ ’(反斜线加上空格)来终止这个十六进制 转义—例如,字符串中的‘\x8e0\ ’代表加上重音符的‘a’。字符串中的‘\ ’就像转义后的换行符 一样,它并不在字符串中产生任何字符,但它可以终止前面的十六进制转义。
对于单字节非ASCII字符,你可以用其字符编码表示它,字符编码必须介于128(八进制的0200)至255(八进制 的0377)。如果你在字符串中写的全部是这种字符,没有其他使得字符串强制变为多字节字符串的字符,则产生一个单字节字符串, 然而。在字符串中使用任何十六进制转义(即使是一个ASCII字符的十六进制转义),也将使字符串强制成为多字符 字符串。
通过‘\u’和‘\U’,你还可以在字符串以字符串的Unicode数值指定字符。(请参考see 字符类型)。
要了解更多关于单字节和多字节的文本表示,请参考See Text Representations.一节。
你可以在字符串中使用和字符文字中相同的反斜线转义序列(但不要使用开启字符常量的?标记)。例如,你可以像"\t, \C-a"
这样写下一个包含非打印字符制表符或C-a,并用逗号和空格分隔它们的字符串。(关于字符的读取语法,请参考See 字符类型.)
然而,并不是所有的反斜线转义序列在字符串中都有有效的。字符串中唯一允许的控制字符即那些ASCII控制字符。字符串不区分 ASCII控制字符的大小写。
恰当地说,字符串不能包含meta字符,但当一个字符串被用作按键序列时,有一个特殊惯例用来在字符串中代表ASCII字符的meta版本。
你可以用‘\M-’语法在字符串常量中表示meta字符。这将设置字符串中该字符的第
2**7
位。如果该字符用于define-key或lookup-key, 这个数值将被转换为相等的meta字符。(请参考See 字符类型.。)
字符串不能持有带有hyper、super或alt修饰的字符。
字符串除持有字符外,还可以持有其存储字符的属性。这使得那些在字符串和缓冲区间拷贝字符的程序可以不费力地拷贝文本属性。要了解对文本属性的 解释,请参考See Text Properties.一节。带有文本属性的字符串使用一个特殊的读取语法:
#("characters" property-data...)
property-data包括0到多个的元素,被分为如下三组:
beg end plist
元素beg和end是整数,它们一起指定了字符串的特定区域;plist是此区域的属性。例如:
#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
代表一个字符串,其文本内容为‘foo bar’,在此字符串,前三个字符具有一个值为bold的face属性,
而后面的三个字符则具有一个值为italic的face属性。(第四个字会没有文本属性,因此它的属性表为nil)。
实际上并不需要指明nil作为属性表,这是因为未在任何区域内提及的字符默认没有任何属性。)
容器是一个包含任意类型元素的一维数组。访问其元素花费的时间固定。(在表中,访问表元素的时间则与元素在表中的位置成比例关系。)
容器的打印表示包含一个左方括号,容器元素,以及一个右方括号。这也是其读取语法。像数字和字符串一样,元素在被当作常量进行求值。
[1 "two" (three)] ; 具有三个元素的容器。
⇒ [1 "two" (three)]
要了解操作容器的函数,请参考See Vectors.一节。
字符表是一个由字符码索引的包含任意类型元素的一维数组。它具有某些额外特性,使其在许多涉及为字符码赋予信息的任务中变得更为有用 —例如,字符表可以具有一个具有默认值的父类,并有少量的槽用于特殊目的。字符表也可以对整个字符集设置单个值。
字符表的打印语法和容器相似,除了在开头有一个额外的‘#^’之外。
要了解操作字符表的特殊函数,请参考See Char-Tables.。
字符表的应用包括:
布尔容器类型是一个元素只能是t或nil的一维数组。
布尔容器的打印语法与字符串相似,除了它由一个‘#&’加上一个长度开始外。后面跟的字符串常量实际上以位图形式指明了布尔容器的
内容—字符串中的每个“字符”包含8个位,用来指尔布尔容器的下8个元素(1代表t,0代表nil)。字符的最低有效位对
应于布尔容器的最小索引。
(make-bool-vector 3 t)
⇒ #&3"^G"
(make-bool-vector 3 nil)
⇒ #&3"^@"
这个结果是有意义的,因为‘C-g’的二进制码为111,而‘C-@’是一个二进制码为0的字符。
如果布尔容器的长度不是8的倍数,其打印表示将显示多余的元素,但这些元素实际上没有意义。例如,在下一个例子中,那两个布尔容器 相等,但只有前三个位有用:
(equal #&3"\377" #&3"\007")
⇒ t
哈希表是一类非常快的查找表,与将关键字映射到值的关联表有几分相似,但更快。其打印表示指明了其属性和内容,像这样:
(make-hash-table)
⇒ #s(hash-table size 65 test eql rehash-size 1.5
rehash-threshold 0.8 data ())
要了解关于哈希表的更多信息,请参考See Hash Tables.。
Lisp函数是可执行的做戏,就像其他语言中的函数一样。在Lisp中,不同于其他语言,函数也是Lisp对象。Lisp中未编译
的函数是一个lambda表达式:即第一个元素的符号lambda的表(请参考see Lambda Expressions.)。
在大多数编程语言中,不可能存在一个没有名字的函数。在Lisp中,函数没有固有的名字。一个lambda表达式可以被当 作函数被调用,即使它没有名字。为了强调这个概念,我们也将这个函数称作匿名函数(请参考see Anonymous Functions)。 Lisp中具有名字的函数只是函数单元具有一个有效函数的符号而已(请参考see Defining Functions)。
大多数情况下,在Lisp程序中,函数以在Lisp表达式中写下其名字地方式被调用。然而,你可以在运行时构造或获取一个函数对
象,然而使用原子函数funccall有apply调用它。(请参考See Calling Functions.)
Lisp宏是一个用户定义的构造器,用来扩充Lisp语言。它由一个像函数的对象表示,但具有不同的参数传递语义。Lisp宏
具有表的形式,该表的第一个元素是符号macro,此表的cdr是一个Lisp函数对象,包括lambda符号。
Lisp宏对象通常使用内置函数defmacro定义,只要Emacs注意到,任何由macro开始的表都是一个宏。关于
如何写作宏,请参考See Macros.。
警告: Lisp宏和键盘宏(参考see Keyboard Macros)是完全不同的事物。当我们未对“宏”这个语做限定时, 我们指一个Lisp宏,而不是键盘宏。
原始函数是一个可被Lisp调用但用C写成的函数。原始函数也被称做子程序(译注:英文subr)或内置函数。(词“subr”派生自 “subroutine”)大多数原始函数在被执行时,将对所有参数进行求值。不对所有参数求值的原始函数称作特殊型(请参考see Special Forms)。
对于调用者而言,函数是否是是原始的并不重要。然而,如果你要尝试用Lisp编写的函数重定义一个原始函数时,你就需要注意了。原因在于原始函数也许 会从C代码中直接调用,对于从Lisp中发起的对于重定义的函数的调用将使用新定义,而从C代码中的调用仍使用原来的函数。
术语function指所有Emacs的函数,无论是用Lisp还是C写成。关于Lisp写成函数的信息,请参考See 函数类型.一节。
原子函数没有读取语法,用哈希记法加上子程序的名字打印。
(symbol-function 'car) ; 访问符号的函数单元 ⇒ #<subr car> (subrp (symbol-function 'car)) ; 是原始函数吗? ⇒ t ; 是。
字节码编译器产生字节码函数对象。从内部来看,一节字节码函数对象更像一个容器;然则 当它以被调用函数的形式出现时, 求值器对这种数据类型进行特殊处理。关于字节码编译器的信息,请参考See Byte Compilation.一节。
字节码函数的打印表示和读取语法像容器一样,但在开始的‘[’之前,有一个附加的‘#’。
自动加载对象是一个第一个元素为符号autoload的表。它做为符号的函数定义存在,为真实的定义占位。自动加载对
象表示真实的定义可以在文件或Lisp代码中找到,并在需要时被加载。它包含文件的名字,以及有关真实定义的某些其他信息。
当文件被加载后,该符号将具有一个一个非自动加载对象的函数。新定义就像一直存在一样被调用。从用户的角度看,函数调用如期望 的那样工作,并使用在加载文件的函数定义。
一个自动加载对象通常使用函数autoload创建,并将该对象存储在符号的函数单元。关于更多细节,请参考See Autoload.。
在前面章节中谈到的类型用于一般的编程需要,它们的大部分在其他Lisp方言中也很常见。Emacs Lisp提供了一些与编辑相关的附加 数据类型,
缓冲区是一个持有可编辑文本的对象(请参考(see Buffers)。大多数缓冲区持有硬盘文件的内容,以便它们可以被编辑, 但某些缓冲区用于其他目的。大多数缓冲区也意味着用户可见,因此某些时候显示在一个窗口里(see Windows.)。 但缓冲并非必需显示 在任何窗口里。每个缓冲区具有一个分配的位置,称作点(请参考see Positions);大多数编辑命令在操作当前缓冲区点周围的 内容。无论何时,只有一个缓冲区是当前缓冲区。
缓冲区的内容和字符串很像,但缓冲区的操作并不像Emacs Lisp中操作字符串一样,它可用的操作是不同的。例如,你可以高效地向既有 的缓冲中插入文本,替换缓冲区内容,而“插入”文本到字符串则需要连结子字符串,而结果是一个全新的字符串对象。
许多标准Emacs函数操作或测试当前缓冲区的字符;本文档专门有整个章节来描述这些函数(请参考see Text)。
每个缓冲区都关联了一些其他数据结构:
局部按键映射和变量表包含用于独立改写全局绑定或值的表项。它们用于定制程序在不同缓冲中的形为,而不影响该程序。
缓冲区可以是间接的,意味着它可以与另一个缓冲共享文本,但用不同的方式呈现。(请参考See Indirect Buffers.)
缓冲区没有读取语法。它们用哈希记法打印,显示缓冲区名。
(current-buffer)
⇒ #<buffer objects.texi>
标记表示特定缓冲区的一个位置。标记具有两个组成部分:一个面向缓冲区,一个面向位置。缓冲区文本发生改变时,将自动重定位 位置值,以便保证标记总是指向缓冲区中相同的两个字符之间。
标记没有读取语法。它们以哈希记法打印,显示当前缓冲区位置以及缓冲区名。
(point-marker)
⇒ #<marker at 10779 in objects.texi>
要了解如何测试、创建、拷贝以及移动标记,请参考See Markers.一节。
窗口描述Emacs用来显示缓冲区使用的终端屏幕的一部分。每个窗口都有一个关联的缓冲区,该缓冲区的内容出现在窗口 上。相反地,一个给定的缓冲区,可以显示在一个窗口里、不在窗口中显示或显示在几个窗口中。
尽管许多窗口可以同时存在,但在任何时候,只有一个窗口被指定为选中窗口。这是在Emacs准备接受命令时,光标通常显示 的窗口。选中窗口通常显示当前缓冲区,但这并不一定。(译注:在编程时,可以使用Lisp操作缓冲区,而该缓冲区不一定是当前缓冲区)。
窗口在屏幕上被分组到框里;每个窗口属于一个且只能属于一个框。请参考See 框类型.。
窗口没有读取语法。它们以哈希记法打印,显示窗口编号以及它显示的缓冲区名。窗口号用于唯一区分窗口,因为指定窗口中的缓冲区 可能频繁变化。
(selected-window)
⇒ #<window 1 on objects.texi>
关于操作窗口函数的描述,请参考See Windows.一节。
框是一个包含一至多个Emacs窗口的屏幕区域;我们也用术语“框”来指Emacs用来指屏幕区域的Lisp对象。
框没有读取语法。它们以哈希记法打印,显示框的标题,以及其在Emacs核心中的地址(用来唯一识别框)。
(selected-frame)
⇒ #<frame emacs@psilocin.gnu.org 0xdac80>
关于操作框函数的描述,请参考See Frames.一节。
终端是一个能够显示一到多个Emacs框的设备(请参考see 框类型)。
终端没有读取语法。它们以哈希记法表示,显示终端的序号以及其TTY设备文件名。
(get-device-terminal nil)
⇒ #<terminal 1 on /dev/tty>
窗口配置一个框中窗口的有关存储位置、大小以及内容的信息,所以你可以后续重新创建相同的窗口布置。
窗口配置没有读取语法;它们的打印语法是‘#<window-configuration>’的形式。关于对与窗口配置相关的 一些函数的描述,请参考See Window Configurations.一节。
框配置存储所有框中窗口的有关存储位置、大小以及内容的信息。它不是一个原始类型—它是一个表,表的car是
frame-configuration并且cdr是一个关联表。关联表的每个元素描述一个框,该框作为该元素的car。
关于对与框配置有关的一些函数的描述,请参考See Frame Configurations.一节。
进程通常意味着一个正在运行的程序。Emacs本身就运行在一个这样的进程中。然而,在Emacs Lisp中,一个进程是一 个被分配了一个Emacs进程创建的子进程的Lisp对象。程序如shells、GDB、ftp以及编译器,运行在Emacs的子进程中,扩展了Emacs 的能力。
所有的Emacs子进程都接受来自Emacs的文本输入,并返回文本输出给Emacs供进一步的吕作。Emacs也可产生信号给这些子进程。
进程对象没有读取语法。它们以哈希记法打印,显示进程的名字。
(process-list)
⇒ (#<process shell>)
关于用来创建、删除、返回信息、发送输入或信号以及接收进程输出的函数的描述,请参考See Processes.一节。
流是一个可以用作字符源或字符接收端的对象—或为输入提供字符或接受字符做为输出。许多不同的类型可以被这样 使用:标记、缓冲区、字符串以及函数。通常,输入流(字符源)从键盘、缓冲区或文件,而发送流(字符接收端)向如*Help*缓冲区 或回显区发送字符。
对象nil,除了它其他的含义外,也可做为流使用。它代表变量standard-input或standard-output。同样的,
对象t也可做为流,代表使用minibuffer(请参考see Minibuffers)的输入,或回显区的输出(请参考see The Echo Area)。
流不具有特殊的打印表示或读取语法,它将以其原始类型打印。
关于与流有关的函数,包括解析或打印函数,请参考See Read and Print.一节。
按键映射将用户的按键映射到命令上。这个映射控制用户命令输入如何执行。一个键盘映射实际上是一个表,该表的car是符号
keymap。
关于创建按键映射、处理前缀按键、本地以及全局按键映射以及改变按键绑定的信息,请参考See Keymaps.一节。
覆盖指定应用于缓冲区的一部分的属性。每个覆盖应用于缓冲区的一个指定范围,包含一个属性表(表的元素是替换的属性名以及属性值) 。覆盖属性用于将缓冲区的部分内容用不同的显示风格进行呈现。覆盖没有读取语法,用哈希记法进行打印,显示缓冲区名字以及位置范围。
关于如何创建覆盖,请参考See Overlays.一节。
字体指定如何在图形终端上显示文本。实际上有三种不同的字体类型—字体对象、字体规格以及字体实体—每 个都具有不同的属性。它们均没有读取语法;它们的打印语法分别是‘#<font-object>’、‘#<font-spec>’以及‘#<font-entity>’ 的形式。关于这些Lisp对象的描述,请参考See Low-Level Font.一节。
为展示复杂Lisp对象中的共享或循环结构,你可以使用‘#n=’和‘#n#’这样的读取构造器。
在对象前使用#n=来标记它供后续引用,后续你可以使用#n#另一个地方来引用该对象。这里的n是一个整数。
例如,下面构造了一个表,在此表中,第一个元素将在第三个元素处再次出现。
(#1=(a) b #1#)
这与一般的如下语法不同
((a) b (a))
此语法产生一个表,表的第一个元素与第三个元素看起来相像,但不是同一个Lisp对象。下面显示其差异:
(prog1 nil
(setq x '(#1=(a) b #1#)))
(eq (nth 0 x) (nth 2 x))
⇒ t
(setq x '((a) b (a)))
(eq (nth 0 x) (nth 2 x))
⇒ nil
你可以使用相同的语法来创建一个循环结构,它自身将作为一个“元素”出现在其自身里。下面是一个例子:
#1=(a #1#)
这将构造一个表,该表的第二个元素是表自身。下面显示它确实能够工作:
(prog1 nil
(setq x '#1=(a #1#)))
(eq x (cadr x))
⇒ t
Lisp打印器可以产生这种语法,用来记录Lisp对象中的循环或共享结构,如果你绑定变量print-circle到一个非nil值。
(请参考See Output Variables.一节)
Emacs Lisp解释器它自身并不在函数调用时对传递给函数的实参进行类型检查。它不能这样做是由于Lisp函数的参数并没有类型声明,像 其他编程语言那样。因此检查每个参数是否属于函数可以使用的类型的工作,需要由单个函数自己完成。
所有的内置函数都检查它们的实际参数,在合适的时候,如果一个参数类型参数,将产生wrong-type-argument错误。例如,
下面是你向+传递一个它不能处理的参数时将会发生的现象:
(+ 2 'a)
error--> Wrong type argument: number-or-marker-p, a
如果你想让你的程序对不同的类型进行不同的处理,你必须进行显式地类型检查。检查对象的类型最常见的方式就是调用一个称为类型判定 的函数。Emacs对每个类型都提供了一个类型判定,以及一些针对组合类型的判定。
类型判定函数接受一个参数;如果参数属于合适的类型,它将返回t,否则返回nil。为遵循Lisp针对类型判定函数的一般惯例,
大多数类型判定名以‘p’结尾。(译注:p是英文predicate的第一个字母。)
下面是使用listp判定来检查表以及symbolp来检查符号的一个例子。
(defun add-on (x)
(cond ((symbolp x)
;; 如果X是一个符号,将其放到表里
(setq list (cons x list)))
((listp x)
;; 如果X是一个表,将其元素插入到表里
(setq list (append x list)))
(t
;; 我们只处理符号和表
(error "Invalid argument %s in add-on" x))))
下面是一个以字母排序的预定义的类型判定表,指向后续的信息。
atomarraypbool-vector-pbufferpbyte-code-function-pcase-table-pchar-or-string-pchar-table-pcommandpconspdisplay-table-pfloatpfontpframe-configuration-pframe-live-pframepfunctionphash-table-pinteger-or-marker-pintegerpkeymappkeywordplistpmarkerpwholenumpnlistpnumberpnumber-or-marker-poverlaypprocesspsequencepstringpsubrpsymbolpsyntax-table-puser-variable-pvectorpwindow-configuration-pwindow-live-pwindowpbooleanpstring-or-null-p检查对象的类型最为普遍的方式就是调用type-of函数。回想一下每个元素都属于一个且仅一个原始类型;type-of告诉
你哪一个原始类型。但type-of并不知道关于非原始类型的任何信息。在大多数情况下,使用类型判定比type-of更为方便。
此函数返回一个命名object所属原始类型的符号。 它的值是如下符号中的一个:
bool-vector,buffer,char-table,compiled-function,cons,float,font-entity,font-object,font-spec,frame,hash-table,integer,marker,overlay,process,string,subr,symbol,vector,window, orwindow-configuration.(type-of 1) ⇒ integer (type-of 'nil) ⇒ symbol (type-of '()) ;()isnil. ⇒ symbol (type-of '(x)) ⇒ cons
下面我们描述用于测试两个对象相等性的函数。 其他函数测试特定类型对象的内容相等性,如字符串。对于这些判定,请参考后续描述 相应数据类型的章节。
如果object1与
object2是同一个对象,此函数返回t,否则返回nil。如果object1与
object2是等值的两个整,eqreturnst。因为符号名通常是唯一的, 如果两个参数是具有同名的符号,它们是eq的。对于其他类型(如表、容器、字符串等),仅仅内容或元素相等并不 使得它们eq对方:它们仅在是同一个对象时是eq的,即意味着内容的修改会在另外一个上反射出来。(eq 'foo 'foo) ⇒ t (eq 456 456) ⇒ t (eq "asdf" "asdf") ⇒ nil (eq "" "") ⇒ t ;; 此特例发生的原因是Emacs Lisp ;; 为了节省空间,只产生一个多字节空字符串。 (eq '(1 (2 (3))) '(1 (2 (3)))) ⇒ nil (setq foo '(1 (2 (3)))) ⇒ (1 (2 (3))) (eq foo foo) ⇒ t (eq foo '(1 (2 (3)))) ⇒ nil (eq [(1 2) 3] [(1 2) 3]) ⇒ nil (eq (point-marker) (point-marker)) ⇒ nil
make-symbol函数产生一个未扣留的符号,不同于你用来在Lisp表达式中写下名字的符号。具有相同名字但不同的符号是不eq的。 (请参考See Creating Symbols.一节)(eq (make-symbol "foo") 'foo) ⇒ nil
如果object1和object2具有相同的内容,此函数返回
t,否则返回nil。eq测试两个参数是否是 同一个对象,而equal查看两个不相等的参数对应的内容是否相同。所以,如果两个对象eq,那么它们也equal,反过来 并不一定成立。(equal 'foo 'foo) ⇒ t (equal 456 456) ⇒ t (equal "asdf" "asdf") ⇒ t (eq "asdf" "asdf") ⇒ nil (equal '(1 (2 (3))) '(1 (2 (3)))) ⇒ t (eq '(1 (2 (3))) '(1 (2 (3)))) ⇒ nil (equal [(1 2) 3] [(1 2) 3]) ⇒ t (eq [(1 2) 3] [(1 2) 3]) ⇒ nil (equal (point-marker) (point-marker)) ⇒ t (eq (point-marker) (point-marker)) ⇒ nil字符串比较是区分大小写的,但并不考虑文本属性—它只比较字符串中的字符。考虑技术层面的原因,仅在具有相同的字符码序列并且 字符码在0到127(ASCII)或160到255(
eight-bit-graphic)范围内,我们可以说一个单字节字符串和多字 节字符串是equal的。(请参考see Text Representations)。(equal "asdf" "ASDF") ⇒ nil然而,两个不同的缓冲区永远不
equal,即使它们的文本内容相同。
相等测试是用递归实现的;如,给定两个cons cellx和y,(equal x y)
仅在下面的两个表达式返回t时返回t:
(equal (car x) (car y))
(equal (cdr x) (cdr y))
由于这种递归方式,循环表因此可能导致无穷循环(导致一个错误)。
此函数在大多数情况下与
equal相似,但要求两个字符串除相等外,它们还必须具有相同的文本属性。(equal "asdf" (propertize "asdf" '(asdf t))) ⇒ t (equal-including-properties "asdf" (propertize "asdf" '(asdf t))) ⇒ nil
GNU Emacs supports two numeric data types: integers and floating point numbers. Integers are whole numbers such as −3, 0, 7, 13, and 511. Their values are exact. Floating point numbers are numbers with fractional parts, such as −4.5, 0.0, or 2.71828. They can also be expressed in exponential notation: 1.5e2 equals 150; in this example, ‘e2’ stands for ten to the second power, and that is multiplied by 1.5. Floating point values are not exact; they have a fixed, limited amount of precision.
The range of values for an integer depends on the machine. The minimum range is −536870912 to 536870911 (30 bits; i.e., -2**29 to 2**29 - 1), but some machines may provide a wider range. Many examples in this chapter assume an integer has 30 bits. The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period.
1 ; The integer 1. 1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer −1. 1073741825 ; Also the integer 1, due to overflow. 0 ; The integer 0. -0 ; The integer 0.
The syntax for integers in bases other than 10 uses ‘#’ followed by a letter that specifies the radix: ‘b’ for binary, ‘o’ for octal, ‘x’ for hex, or ‘radixr’ to specify radix radix. Case is not significant for the letter that specifies the radix. Thus, ‘#binteger’ reads integer in binary, and ‘#radixrinteger’ reads integer in radix radix. Allowed values of radix run from 2 to 36. For example:
#b101100 ⇒ 44
#o54 ⇒ 44
#x2c ⇒ 44
#24r1k ⇒ 44
To understand how various functions work on integers, especially the bitwise operators (see Bitwise Operations), it is often helpful to view the numbers in their binary form.
In 30-bit binary, the decimal integer 5 looks like this:
00 0000 0000 0000 0000 0000 0000 0101
(We have inserted spaces between groups of 4 bits, and two spaces between groups of 8 bits, to make the binary integer easier to read.)
The integer −1 looks like this:
11 1111 1111 1111 1111 1111 1111 1111
−1 is represented as 30 ones. (This is called two's complement notation.)
The negative integer, −5, is creating by subtracting 4 from −1. In binary, the decimal integer 4 is 100. Consequently, −5 looks like this:
11 1111 1111 1111 1111 1111 1111 1011
In this implementation, the largest 30-bit binary integer value is 536,870,911 in decimal. In binary, it looks like this:
01 1111 1111 1111 1111 1111 1111 1111
Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 536,870,911, the value is the negative integer −536,870,912:
(+ 1 536870911)
⇒ -536870912
⇒ 10 0000 0000 0000 0000 0000 0000 0000
Many of the functions described in this chapter accept markers for arguments in place of numbers. (See Markers.) Since the actual arguments to such functions may be either numbers or markers, we often give these arguments the name number-or-marker. When the argument value is a marker, its position value is used and its buffer is ignored.
The value of this variable is the largest integer that Emacs Lisp can handle.
The value of this variable is the smallest integer that Emacs Lisp can handle. It is negative.
See max-char, for the maximum value of a valid character codepoint.
Floating point numbers are useful for representing numbers that are
not integral. The precise range of floating point numbers is
machine-specific; it is the same as the range of the C data type
double on the machine you are using.
The read-syntax for floating point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, ‘1500.0’, ‘15e2’, ‘15.0e2’, ‘1.5e3’, and ‘.15e4’ are five ways of writing a floating point number whose value is 1500. They are all equivalent. You can also use a minus sign to write negative floating point numbers, as in ‘-1.0’.
Most modern computers support the IEEE floating point standard,
which provides for positive infinity and negative infinity as floating point
values. It also provides for a class of values called NaN or
“not-a-number”; numerical functions return such values in cases where
there is no correct answer. For example, (/ 0.0 0.0) returns a
NaN. For practical purposes, there's no significant difference between
different NaN values in Emacs Lisp, and there's no rule for precisely
which NaN value should be used in a particular case, so Emacs Lisp
doesn't try to distinguish them (but it does report the sign, if you
print it). Here are the read syntaxes for these special floating
point values:
To test whether a floating point value is a NaN, compare it with
itself using =. That returns nil for a NaN, and
t for any other floating point value.
The value -0.0 is distinguishable from ordinary zero in
IEEE floating point, but Emacs Lisp equal and
= consider them equal values.
You can use logb to extract the binary exponent of a floating
point number (or estimate the logarithm of an integer):
This function returns the binary exponent of number. More precisely, the value is the logarithm of number base 2, rounded down to an integer.
(logb 10) ⇒ 3 (logb 10.0e20) ⇒ 69
The functions in this section test for numbers, or for a specific
type of number. The functions integerp and floatp can
take any type of Lisp object as argument (they would not be of much
use otherwise), but the zerop predicate requires a number as
its argument. See also integer-or-marker-p and
number-or-marker-p, in Predicates on Markers.
This predicate tests whether its argument is a floating point number and returns
tif so,nilotherwise.
floatpdoes not exist in Emacs versions 18 and earlier.
This predicate tests whether its argument is an integer, and returns
tif so,nilotherwise.
This predicate tests whether its argument is a number (either integer or floating point), and returns
tif so,nilotherwise.
The
wholenumppredicate (whose name comes from the phrase “whole-number-p”) tests to see whether its argument is a nonnegative integer, and returnstif so,nilotherwise. 0 is considered non-negative.
This predicate tests whether its argument is zero, and returns
tif so,nilotherwise. The argument must be a number.
(zerop x)is equivalent to(= x 0).
To test numbers for numerical equality, you should normally use
=, not eq. There can be many distinct floating point
number objects with the same numeric value. If you use eq to
compare them, then you test whether two values are the same
object. By contrast, = compares only the numeric values
of the objects.
At present, each integer value has a unique Lisp object in Emacs Lisp.
Therefore, eq is equivalent to = where integers are
concerned. It is sometimes convenient to use eq for comparing an
unknown value with an integer, because eq does not report an
error if the unknown value is not a number—it accepts arguments of any
type. By contrast, = signals an error if the arguments are not
numbers or markers. However, it is a good idea to use = if you
can, even for comparing integers, just in case we change the
representation of integers in a future Emacs version.
Sometimes it is useful to compare numbers with equal; it
treats two numbers as equal if they have the same data type (both
integers, or both floating point) and the same value. By contrast,
= can treat an integer and a floating point number as equal.
See 相等判定.
There is another wrinkle: because floating point arithmetic is not exact, it is often a bad idea to check for equality of two floating point values. Usually it is better to test for approximate equality. Here's a function to do this:
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (and (= x 0) (= y 0))
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
Common Lisp note: Comparing numbers in Common Lisp always requires
= because Common Lisp implements multi-word integers, and two
distinct integer objects can have the same numeric value. Emacs Lisp
can have just one integer object for any given value because it has a
limited range of integer values.
This function tests whether its arguments are numerically equal, and returns
tif so,nilotherwise.
This function acts like
eqexcept when both arguments are numbers. It compares numbers by type and numeric value, so that(eql 1.0 1)returnsnil, but(eql 1.0 1.0)and(eql 1 1)both returnt.
This function tests whether its arguments are numerically equal, and returns
tif they are not, andnilif they are.
This function tests whether its first argument is strictly less than its second argument. It returns
tif so,nilotherwise.
This function tests whether its first argument is less than or equal to its second argument. It returns
tif so,nilotherwise.
This function tests whether its first argument is strictly greater than its second argument. It returns
tif so,nilotherwise.
This function tests whether its first argument is greater than or equal to its second argument. It returns
tif so,nilotherwise.
This function returns the largest of its arguments. If any of the arguments is floating-point, the value is returned as floating point, even if it was given as an integer.
(max 20) ⇒ 20 (max 1 2.5) ⇒ 2.5 (max 1 3 2.5) ⇒ 3.0
This function returns the smallest of its arguments. If any of the arguments is floating-point, the value is returned as floating point, even if it was given as an integer.
(min -4 1) ⇒ -4
To convert an integer to floating point, use the function float.
This returns number converted to floating point. If number is already a floating point number,
floatreturns it unchanged.
There are four functions to convert floating point numbers to integers;
they differ in how they round. All accept an argument number
and an optional argument divisor. Both arguments may be
integers or floating point numbers. divisor may also be
nil. If divisor is nil or omitted, these
functions convert number to an integer, or return it unchanged
if it already is an integer. If divisor is non-nil, they
divide number by divisor and convert the result to an
integer. An arith-error results if divisor is 0.
This returns number, converted to an integer by rounding towards zero.
(truncate 1.2) ⇒ 1 (truncate 1.7) ⇒ 1 (truncate -1.2) ⇒ -1 (truncate -1.7) ⇒ -1
This returns number, converted to an integer by rounding downward (towards negative infinity).
If divisor is specified, this uses the kind of division operation that corresponds to
mod, rounding downward.(floor 1.2) ⇒ 1 (floor 1.7) ⇒ 1 (floor -1.2) ⇒ -2 (floor -1.7) ⇒ -2 (floor 5.99 3) ⇒ 1
This returns number, converted to an integer by rounding upward (towards positive infinity).
(ceiling 1.2) ⇒ 2 (ceiling 1.7) ⇒ 2 (ceiling -1.2) ⇒ -1 (ceiling -1.7) ⇒ -1
This returns number, converted to an integer by rounding towards the nearest integer. Rounding a value equidistant between two integers may choose the integer closer to zero, or it may prefer an even integer, depending on your machine.
(round 1.2) ⇒ 1 (round 1.7) ⇒ 2 (round -1.2) ⇒ -1 (round -1.7) ⇒ -2
Emacs Lisp provides the traditional four arithmetic operations: addition, subtraction, multiplication, and division. Remainder and modulus functions supplement the division functions. The functions to add or subtract 1 are provided because they are traditional in Lisp and commonly used.
All of these functions except % return a floating point value
if any argument is floating.
It is important to note that in Emacs Lisp, arithmetic functions
do not check for overflow. Thus (1+ 268435455) may evaluate to
−268435456, depending on your hardware.
This function returns number-or-marker plus 1. For example,
(setq foo 4) ⇒ 4 (1+ foo) ⇒ 5This function is not analogous to the C operator
++—it does not increment a variable. It just computes a sum. Thus, if we continue,foo ⇒ 4If you want to increment the variable, you must use
setq, like this:(setq foo (1+ foo)) ⇒ 5
This function adds its arguments together. When given no arguments,
+returns 0.(+) ⇒ 0 (+ 1) ⇒ 1 (+ 1 2 3 4) ⇒ 10
The
-function serves two purposes: negation and subtraction. When-has a single argument, the value is the negative of the argument. When there are multiple arguments,-subtracts each of the more-numbers-or-markers from number-or-marker, cumulatively. If there are no arguments, the result is 0.(- 10 1 2 3 4) ⇒ 0 (- 10) ⇒ -10 (-) ⇒ 0
This function multiplies its arguments together, and returns the product. When given no arguments,
*returns 1.(*) ⇒ 1 (* 1) ⇒ 1 (* 1 2 3 4) ⇒ 24
This function divides dividend by divisor and returns the quotient. If there are additional arguments divisors, then it divides dividend by each divisor in turn. Each argument may be a number or a marker.
If all the arguments are integers, then the result is an integer too. This means the result has to be rounded. On most machines, the result is rounded towards zero after each division, but some machines may round differently with negative arguments. This is because the Lisp function
/is implemented using the C division operator, which also permits machine-dependent rounding. As a practical matter, all known machines round in the standard fashion.If you divide an integer by 0, an
arith-errorerror is signaled. (See Errors.) Floating point division by zero returns either infinity or a NaN if your machine supports IEEE floating point; otherwise, it signals anarith-errorerror.(/ 6 2) ⇒ 3 (/ 5 2) ⇒ 2 (/ 5.0 2) ⇒ 2.5 (/ 5 2.0) ⇒ 2.5 (/ 5.0 2.0) ⇒ 2.5 (/ 25 3 2) ⇒ 4 (/ -17 6) ⇒ -2 (could in theory be −3 on some machines)
This function returns the integer remainder after division of dividend by divisor. The arguments must be integers or markers.
For negative arguments, the remainder is in principle machine-dependent since the quotient is; but in practice, all known machines behave alike.
An
arith-errorresults if divisor is 0.(% 9 4) ⇒ 1 (% -9 4) ⇒ -1 (% 9 -4) ⇒ 1 (% -9 -4) ⇒ -1For any two integers dividend and divisor,
(+ (% dividend divisor) (* (/ dividend divisor) divisor))always equals dividend.
This function returns the value of dividend modulo divisor; in other words, the remainder after division of dividend by divisor, but with the same sign as divisor. The arguments must be numbers or markers.
Unlike
%,modreturns a well-defined result for negative arguments. It also permits floating point arguments; it rounds the quotient downward (towards minus infinity) to an integer, and uses that quotient to compute the remainder.An
arith-errorresults if divisor is 0.(mod 9 4) ⇒ 1 (mod -9 4) ⇒ 3 (mod 9 -4) ⇒ -3 (mod -9 -4) ⇒ -1 (mod 5.5 2.5) ⇒ .5For any two numbers dividend and divisor,
(+ (mod dividend divisor) (* (floor dividend divisor) divisor))always equals dividend, subject to rounding error if either argument is floating point. For
floor, see Numeric Conversions.
The functions ffloor, fceiling, fround, and
ftruncate take a floating point argument and return a floating
point result whose value is a nearby integer. ffloor returns the
nearest integer below; fceiling, the nearest integer above;
ftruncate, the nearest integer in the direction towards zero;
fround, the nearest integer.
This function rounds float to the next lower integral value, and returns that value as a floating point number.
This function rounds float to the next higher integral value, and returns that value as a floating point number.
This function rounds float towards zero to an integral value, and returns that value as a floating point number.
This function rounds float to the nearest integral value, and returns that value as a floating point number.
In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern “moved over.”
The bitwise operations in Emacs Lisp apply only to integers.
lsh, which is an abbreviation for logical shift, shifts the bits in integer1 to the left count places, or to the right if count is negative, bringing zeros into the vacated bits. If count is negative,lshshifts zeros into the leftmost (most-significant) bit, producing a positive result even if integer1 is negative. Contrast this withash, below.Here are two examples of
lsh, shifting a pattern of bits one place to the left. We show only the low-order eight bits of the binary pattern; the rest are all zero.(lsh 5 1) ⇒ 10 ;; Decimal 5 becomes decimal 10. 00000101 ⇒ 00001010 (lsh 7 1) ⇒ 14 ;; Decimal 7 becomes decimal 14. 00000111 ⇒ 00001110As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.
Shifting a pattern of bits two places to the left produces results like this (with 8-bit binary numbers):
(lsh 3 2) ⇒ 12 ;; Decimal 3 becomes decimal 12. 00000011 ⇒ 00001100On the other hand, shifting one place to the right looks like this:
(lsh 6 -1) ⇒ 3 ;; Decimal 6 becomes decimal 3. 00000110 ⇒ 00000011 (lsh 5 -1) ⇒ 2 ;; Decimal 5 becomes decimal 2. 00000101 ⇒ 00000010As the example illustrates, shifting one place to the right divides the value of a positive integer by two, rounding downward.
The function
lsh, like all Emacs Lisp arithmetic functions, does not check for overflow, so shifting left can discard significant bits and change the sign of the number. For example, left shifting 536,870,911 produces −2 on a 30-bit machine:(lsh 536870911 1) ; left shift ⇒ -2In binary, in the 30-bit implementation, the argument looks like this:
;; Decimal 536,870,911 01 1111 1111 1111 1111 1111 1111 1111which becomes the following when left shifted:
;; Decimal −2 11 1111 1111 1111 1111 1111 1111 1110
ash(arithmetic shift) shifts the bits in integer1 to the left count places, or to the right if count is negative.
ashgives the same results aslshexcept when integer1 and count are both negative. In that case,ashputs ones in the empty bit positions on the left, whilelshputs zeros in those bit positions.Thus, with
ash, shifting the pattern of bits one place to the right looks like this:(ash -6 -1) ⇒ -3 ;; Decimal −6 becomes decimal −3. 11 1111 1111 1111 1111 1111 1111 1010 ⇒ 11 1111 1111 1111 1111 1111 1111 1101In contrast, shifting the pattern of bits one place to the right with
lshlooks like this:(lsh -6 -1) ⇒ 536870909 ;; Decimal −6 becomes decimal 536,870,909. 11 1111 1111 1111 1111 1111 1111 1010 ⇒ 01 1111 1111 1111 1111 1111 1111 1101Here are other examples:
; 30-bit binary values (lsh 5 2) ; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ⇒ 20 ; = 00 0000 0000 0000 0000 0000 0001 0100 (ash 5 2) ⇒ 20 (lsh -5 2) ; -5 = 11 1111 1111 1111 1111 1111 1111 1011 ⇒ -20 ; = 11 1111 1111 1111 1111 1111 1110 1100 (ash -5 2) ⇒ -20 (lsh 5 -2) ; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ⇒ 1 ; = 00 0000 0000 0000 0000 0000 0000 0001 (ash 5 -2) ⇒ 1 (lsh -5 -2) ; -5 = 11 1111 1111 1111 1111 1111 1111 1011 ⇒ 268435454 ; = 00 0111 1111 1111 1111 1111 1111 1110 (ash -5 -2) ; -5 = 11 1111 1111 1111 1111 1111 1111 1011 ⇒ -2 ; = 11 1111 1111 1111 1111 1111 1111 1110
This function returns the “logical and” of the arguments: the nth bit is set in the result if, and only if, the nth bit is set in all the arguments. (“Set” means that the value of the bit is 1 rather than 0.)
For example, using 4-bit binary numbers, the “logical and” of 13 and 12 is 12: 1101 combined with 1100 produces 1100. In both the binary numbers, the leftmost two bits are set (i.e., they are 1's), so the leftmost two bits of the returned value are set. However, for the rightmost two bits, each is zero in at least one of the arguments, so the rightmost two bits of the returned value are 0's.
Therefore,
(logand 13 12) ⇒ 12If
logandis not passed any argument, it returns a value of −1. This number is an identity element forlogandbecause its binary representation consists entirely of ones. Iflogandis passed just one argument, it returns that argument.; 30-bit binary values (logand 14 13) ; 14 = 00 0000 0000 0000 0000 0000 0000 1110 ; 13 = 00 0000 0000 0000 0000 0000 0000 1101 ⇒ 12 ; 12 = 00 0000 0000 0000 0000 0000 0000 1100 (logand 14 13 4) ; 14 = 00 0000 0000 0000 0000 0000 0000 1110 ; 13 = 00 0000 0000 0000 0000 0000 0000 1101 ; 4 = 00 0000 0000 0000 0000 0000 0000 0100 ⇒ 4 ; 4 = 00 0000 0000 0000 0000 0000 0000 0100 (logand) ⇒ -1 ; -1 = 11 1111 1111 1111 1111 1111 1111 1111
This function returns the “inclusive or” of its arguments: the nth bit is set in the result if, and only if, the nth bit is set in at least one of the arguments. If there are no arguments, the result is zero, which is an identity element for this operation. If
logioris passed just one argument, it returns that argument.; 30-bit binary values (logior 12 5) ; 12 = 00 0000 0000 0000 0000 0000 0000 1100 ; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ⇒ 13 ; 13 = 00 0000 0000 0000 0000 0000 0000 1101 (logior 12 5 7) ; 12 = 00 0000 0000 0000 0000 0000 0000 1100 ; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ; 7 = 00 0000 0000 0000 0000 0000 0000 0111 ⇒ 15 ; 15 = 00 0000 0000 0000 0000 0000 0000 1111
This function returns the “exclusive or” of its arguments: the nth bit is set in the result if, and only if, the nth bit is set in an odd number of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If
logxoris passed just one argument, it returns that argument.; 30-bit binary values (logxor 12 5) ; 12 = 00 0000 0000 0000 0000 0000 0000 1100 ; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ⇒ 9 ; 9 = 00 0000 0000 0000 0000 0000 0000 1001 (logxor 12 5 7) ; 12 = 00 0000 0000 0000 0000 0000 0000 1100 ; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ; 7 = 00 0000 0000 0000 0000 0000 0000 0111 ⇒ 14 ; 14 = 00 0000 0000 0000 0000 0000 0000 1110
This function returns the logical complement of its argument: the nth bit is one in the result if, and only if, the nth bit is zero in integer, and vice-versa.
(lognot 5) ⇒ -6 ;; 5 = 00 0000 0000 0000 0000 0000 0000 0101 ;; becomes ;; -6 = 11 1111 1111 1111 1111 1111 1111 1010
These mathematical functions allow integers as well as floating point numbers as arguments.
These are the ordinary trigonometric functions, with argument measured in radians.
The value of
(asinarg)is a number between −pi/2 and pi/2 (inclusive) whose sine is arg; if, however, arg is out of range (outside [−1, 1]), it signals adomain-errorerror.
The value of
(acosarg)is a number between 0 and pi (inclusive) whose cosine is arg; if, however, arg is out of range (outside [−1, 1]), it signals adomain-errorerror.
The value of
(atany)is a number between −pi/2 and pi/2 (exclusive) whose tangent is y. If the optional second argument x is given, the value of(atan y x)is the angle in radians between the vector[x,y]and theXaxis.
This is the exponential function; it returns e to the power arg. e is a fundamental mathematical constant also called the base of natural logarithms.
This function returns the logarithm of arg, with base base. If you don't specify base, the base e is used. If arg is negative, it signals a
domain-errorerror.
This function returns the logarithm of arg, with base 10. If arg is negative, it signals a
domain-errorerror.(log10x)==(logx10), at least approximately.
This function returns x raised to power y. If both arguments are integers and y is positive, the result is an integer; in this case, overflow causes truncation, so watch out.
This returns the square root of arg. If arg is negative, it signals a
domain-errorerror.
A deterministic computer program cannot generate true random numbers. For most purposes, pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series.
In Emacs, pseudo-random numbers are generated from a “seed” number.
Starting from any given seed, the random function always
generates the same sequence of numbers. Emacs always starts with the
same seed value, so the sequence of values of random is actually
the same in each Emacs run! For example, in one operating system, the
first call to (random) after you start Emacs always returns
−1457731, and the second one always returns −7692030. This
repeatability is helpful for debugging.
If you want random numbers that don't always come out the same, execute
(random t). This chooses a new seed based on the current time of
day and on Emacs's process ID number.
This function returns a pseudo-random integer. Repeated calls return a series of pseudo-random integers.
If limit is a positive integer, the value is chosen to be nonnegative and less than limit.
If limit is
t, it means to choose a new seed based on the current time of day and on Emacs's process ID number.On some machines, any integer representable in Lisp may be the result of
random. On other machines, the result can never be larger than a certain maximum or less than a certain (negative) minimum.
A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files; to send messages to users; to hold text being copied between buffers; and for many other purposes. Because strings are so important, Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters.
See Strings of Events, for special considerations for strings of keyboard character events.
Characters are represented in Emacs Lisp as integers; whether an integer is a character or not is determined only by how it is used. Thus, strings really contain integers. See Character Codes, for details about character representation in Emacs.
The length of a string (like any array) is fixed, and cannot be altered once the string exists. Strings in Lisp are not terminated by a distinguished character code. (By contrast, strings in C are terminated by a character with ASCII code 0.)
Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions.
(See Sequences Arrays Vectors.) For example, you can access or
change individual characters in a string using the functions aref
and aset (see Array Functions).
There are two text representations for non-ASCII characters in Emacs strings (and in buffers): unibyte and multibyte (see Text Representations). For most Lisp programming, you don't need to be concerned with these two representations.
Sometimes key sequences are represented as unibyte strings. When a unibyte string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are large integers) rather than character codes in the range 128 to 255. Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no other control characters. They do not distinguish case in ASCII control characters. If you want to store such characters in a sequence, such as a key sequence, you must use a vector instead of a string. See 字符类型, for more information about keyboard input characters.
Strings are useful for holding regular expressions. You can also
match regular expressions against strings with string-match
(see Regexp Search). The functions match-string
(see Simple Match Data) and replace-match (see Replacing Match) are useful for decomposing and modifying strings after
matching regular expressions against them.
Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See Text Properties. All the Lisp primitives that copy text from strings to buffers or other strings also copy the properties of the characters being copied.
See Text, for information about functions that display strings or copy them into buffers. See 字符类型, and 字符串类型, for information about the syntax of characters and strings. See Non-ASCII Characters, for functions to convert between text representations and to encode and decode character codes.
For more information about general sequence and array predicates, see Sequences Arrays Vectors, and Arrays.
This function returns
tif object is a string ornil. It returnsnilotherwise.
This function returns
tif object is a string or a character (i.e., an integer),nilotherwise.
The following functions create strings, either from scratch, or by putting strings together, or by taking them apart.
This function returns a string made up of count repetitions of character. If count is negative, an error is signaled.
(make-string 5 ?x) ⇒ "xxxxx" (make-string 0 ?x) ⇒ ""Other functions to compare with this one include
make-vector(see Vectors) andmake-list(see Building Lists).
This returns a string containing the characters characters.
(string ?a ?b ?c) ⇒ "abc"
This function returns a new string which consists of those characters from string in the range from (and including) the character at the index start up to (but excluding) the character at the index end. The first character is at index zero.
(substring "abcdefg" 0 3) ⇒ "abc"In the above example, the index for ‘a’ is 0, the index for ‘b’ is 1, and the index for ‘c’ is 2. The index 3—which is the fourth character in the string—marks the character position up to which the substring is copied. Thus, ‘abc’ is copied from the string
"abcdefg".A negative number counts from the end of the string, so that −1 signifies the index of the last character of the string. For example:
(substring "abcdefg" -3 -1) ⇒ "ef"In this example, the index for ‘e’ is −3, the index for ‘f’ is −2, and the index for ‘g’ is −1. Therefore, ‘e’ and ‘f’ are included, and ‘g’ is excluded.
When
nilis used for end, it stands for the length of the string. Thus,(substring "abcdefg" -3 nil) ⇒ "efg"Omitting the argument end is equivalent to specifying
nil. It follows that(substringstring0)returns a copy of all of string.(substring "abcdefg" 0) ⇒ "abcdefg"But we recommend
copy-sequencefor this purpose (see Sequence Functions).If the characters copied from string have text properties, the properties are copied into the new string also. See Text Properties.
substringalso accepts a vector for the first argument. For example:(substring [a b (c) "d"] 1 3) ⇒ [b (c)]A
wrong-type-argumenterror is signaled if start is not an integer or if end is neither an integer nornil. Anargs-out-of-rangeerror is signaled if start indicates a character following end, or if either integer is out of range for string.Contrast this function with
buffer-substring(see Buffer Contents), which returns a string containing a portion of the text in the current buffer. The beginning of a string is at index 0, but the beginning of a buffer is at index 1.
This works like
substringbut discards all text properties from the value. Also, start may be omitted ornil, which is equivalent to 0. Thus,(substring-no-propertiesstring)returns a copy of string, with all text properties removed.
This function returns a new string consisting of the characters in the arguments passed to it (along with their text properties, if any). The arguments may be strings, lists of numbers, or vectors of numbers; they are not themselves changed. If
concatreceives no arguments, it returns an empty string.(concat "abc" "-def") ⇒ "abc-def" (concat "abc" (list 120 121) [122]) ⇒ "abcxyz" ;;nilis an empty sequence. (concat "abc" nil "-def") ⇒ "abc-def" (concat "The " "quick brown " "fox.") ⇒ "The quick brown fox." (concat) ⇒ ""This function always constructs a new string that is not
eqto any existing string, except when the result is the empty string (to save space, Emacs makes only one empty multibyte string).For information about other concatenation functions, see the description of
mapconcatin Mapping Functions,vconcatin Vector Functions, andappendin Building Lists. For concatenating individual command-line arguments into a string to be used as a shell command, see combine-and-quote-strings.
This function splits string into substrings based on the regular expression separators (see Regular Expressions). Each match for separators defines a splitting point; the substrings between splitting points are made into a list, which is returned.
If omit-nulls is
nil(or omitted), the result contains null strings whenever there are two consecutive matches for separators, or a match is adjacent to the beginning or end of string. If omit-nulls ist, these null strings are omitted from the result.If separators is
nil(or omitted), the default is the value ofsplit-string-default-separators.As a special case, when separators is
nil(or omitted), null strings are always omitted from the result. Thus:(split-string " two words ") ⇒ ("two" "words")The result is not
("" "two" "words" ""), which would rarely be useful. If you need such a result, use an explicit value for separators:(split-string " two words " split-string-default-separators) ⇒ ("" "two" "words" "")More examples:
(split-string "Soup is good food" "o") ⇒ ("S" "up is g" "" "d f" "" "d") (split-string "Soup is good food" "o" t) ⇒ ("S" "up is g" "d f" "d") (split-string "Soup is good food" "o+") ⇒ ("S" "up is g" "d f" "d")Empty matches do count, except that
split-stringwill not look for a final empty match when it already reached the end of the string using a non-empty match or when string is empty:(split-string "aooob" "o*") ⇒ ("" "a" "" "b" "") (split-string "ooaboo" "o*") ⇒ ("" "" "a" "b" "") (split-string "" "") ⇒ ("")However, when separators can match the empty string, omit-nulls is usually
t, so that the subtleties in the three previous examples are rarely relevant:(split-string "Soup is good food" "o*" t) ⇒ ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") (split-string "Nice doggy!" "" t) ⇒ ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!") (split-string "" "" t) ⇒ nilSomewhat odd, but predictable, behavior can occur for certain “non-greedy” values of separators that can prefer empty matches over non-empty matches. Again, such values rarely occur in practice:
(split-string "ooo" "o*" t) ⇒ nil (split-string "ooo" "\\|o+" t) ⇒ ("o" "o" "o")If you need to split a string into a list of individual command-line arguments suitable for
call-processorstart-process, see split-string-and-unquote.
The default value of separators for
split-string. Its usual value is"[ \f\t\n\r\v]+".
The most basic way to alter the contents of an existing string is with
aset (see Array Functions). (aset string
idx char) stores char into string at index
idx. Each character occupies one or more bytes, and if char
needs a different number of bytes from the character already present at
that index, aset signals an error.
A more powerful function is store-substring:
This function alters part of the contents of the string string, by storing obj starting at index idx. The argument obj may be either a character or a (smaller) string.
Since it is impossible to change the length of an existing string, it is an error if obj doesn't fit within string's actual length, or if any new character requires a different number of bytes from the character currently present at that point in string.
To clear out a string that contained a password, use
clear-string:
This makes string a unibyte string and clears its contents to zeros. It may also change string's length.
This function returns
tif the arguments represent the same character,nilotherwise. This function ignores differences in case ifcase-fold-searchis non-nil.(char-equal ?x ?x) ⇒ t (let ((case-fold-search nil)) (char-equal ?x ?X)) ⇒ nil
This function returns
tif the characters of the two strings match exactly. Symbols are also allowed as arguments, in which case their print names are used. Case is always significant, regardless ofcase-fold-search.(string= "abc" "abc") ⇒ t (string= "abc" "ABC") ⇒ nil (string= "ab" "ABC") ⇒ nilThe function
string=ignores the text properties of the two strings. Whenequal(see 相等判定) compares two strings, it usesstring=.For technical reasons, a unibyte and a multibyte string are
equalif and only if they contain the same sequence of character codes and all these codes are either in the range 0 through 127 (ASCII) or 160 through 255 (eight-bit-graphic). However, when a unibyte string is converted to a multibyte string, all characters with codes in the range 160 through 255 are converted to characters with higher codes, whereas ASCII characters remain unchanged. Thus, a unibyte string and its conversion to multibyte are onlyequalif the string is all ASCII. Character codes 160 through 255 are not entirely proper in multibyte text, even though they can occur. As a consequence, the situation where a unibyte and a multibyte string areequalwithout both being all ASCII is a technical oddity that very few Emacs Lisp programmers ever get confronted with. See Text Representations.
This function compares two strings a character at a time. It scans both the strings at the same time to find the first pair of corresponding characters that do not match. If the lesser character of these two is the character from string1, then string1 is less, and this function returns
t. If the lesser character is the one from string2, then string1 is greater, and this function returnsnil. If the two strings match entirely, the value isnil.Pairs of characters are compared according to their character codes. Keep in mind that lower case letters have higher numeric values in the ASCII character set than their upper case counterparts; digits and many punctuation characters have a lower numeric value than upper case letters. An ASCII character is less than any non-ASCII character; a unibyte non-ASCII character is always less than any multibyte non-ASCII character (see Text Representations).
(string< "abc" "abd") ⇒ t (string< "abd" "abc") ⇒ nil (string< "123" "abc") ⇒ tWhen the strings have different lengths, and they match up to the length of string1, then the result is
t. If they match up to the length of string2, the result isnil. A string of no characters is less than any other string.(string< "" "abc") ⇒ t (string< "ab" "abc") ⇒ t (string< "abc" "") ⇒ nil (string< "abc" "ab") ⇒ nil (string< "" "") ⇒ nilSymbols are also allowed as arguments, in which case their print names are used.
This function compares the specified part of string1 with the specified part of string2. The specified part of string1 runs from index start1 up to index end1 (
nilmeans the end of the string). The specified part of string2 runs from index start2 up to index end2 (nilmeans the end of the string).The strings are both converted to multibyte for the comparison (see Text Representations) so that a unibyte string and its conversion to multibyte are always regarded as equal. If ignore-case is non-
nil, then case is ignored, so that upper case letters can be equal to lower case letters.If the specified portions of the two strings match, the value is
t. Otherwise, the value is an integer which indicates how many leading characters agree, and which string is less. Its absolute value is one plus the number of characters that agree at the beginning of the two strings. The sign is negative if string1 (or its specified portion) is less.
This function works like
assoc, except that key must be a string or symbol, and comparison is done usingcompare-strings. Symbols are converted to strings before testing. If case-fold is non-nil, it ignores case differences. Unlikeassoc, this function can also match elements of the alist that are strings or symbols rather than conses. In particular, alist can be a list of strings or symbols rather than an actual alist. See Association Lists.
See also the function compare-buffer-substrings in
Comparing Text, for a way to compare text in buffers. The
function string-match, which matches a regular expression
against a string, can be used for a kind of string comparison; see
Regexp Search.
This section describes functions for converting between characters,
strings and integers. format (see Formatting Strings) and
prin1-to-string (see Output Functions) can also convert
Lisp objects into strings. read-from-string (see Input Functions) can “convert” a string representation of a Lisp object
into an object. The functions string-make-multibyte and
string-make-unibyte convert the text representation of a string
(see Converting Representations).
See Documentation, for functions that produce textual descriptions
of text characters and general input events
(single-key-description and text-char-description). These
are used primarily for making help messages.
This function returns a string consisting of the printed base-ten representation of number, which may be an integer or a floating point number. The returned value starts with a minus sign if the argument is negative.
(number-to-string 256) ⇒ "256" (number-to-string -23) ⇒ "-23" (number-to-string -23.5) ⇒ "-23.5"
int-to-stringis a semi-obsolete alias for this function.See also the function
formatin Formatting Strings.
This function returns the numeric value of the characters in string. If base is non-
nil, it must be an integer between 2 and 16 (inclusive), and integers are converted in that base. If base isnil, then base ten is used. Floating point conversion only works in base ten; we have not implemented other radices for floating point numbers, because that would be much more work and does not seem useful. If string looks like an integer but its value is too large to fit into a Lisp integer,string-to-numberreturns a floating point result.The parsing skips spaces and tabs at the beginning of string, then reads as much of string as it can interpret as a number in the given base. (On some systems it ignores other whitespace at the beginning, not just spaces and tabs.) If the first character after the ignored whitespace is neither a digit in the given base, nor a plus or minus sign, nor the leading dot of a floating point number, this function returns 0.
(string-to-number "256") ⇒ 256 (string-to-number "25 is a perfect square.") ⇒ 25 (string-to-number "X256") ⇒ 0 (string-to-number "-4.5") ⇒ -4.5 (string-to-number "1e5") ⇒ 100000.0
This function returns a new string containing one character, character. This function is semi-obsolete because the function
stringis more general. See Creating Strings.
This function returns the first character in string. This mostly identical to
(aref string 0), except that it returns 0 if the string is empty. (The value is also 0 when the first character of string is the null character, ASCII code 0.) This function may be eliminated in the future if it does not seem useful enough to retain.
Here are some other functions that can convert to or from a string:
concatvconcatappendbyte-to-stringFormatting means constructing a string by substituting computed values at various places in a constant string. This constant string controls how the other values are printed, as well as where they appear; it is called a format string.
Formatting is often useful for computing messages to be displayed. In
fact, the functions message and error provide the same
formatting feature described here; they differ from format only
in how they use the result of formatting.
This function returns a new string that is made by copying string and then replacing any format specification in the copy with encodings of the corresponding objects. The arguments objects are the computed values to be formatted.
The characters in string, other than the format specifications, are copied directly into the output, including their text properties, if any.
A format specification is a sequence of characters beginning with a
‘%’. Thus, if there is a ‘%d’ in string, the
format function replaces it with the printed representation of
one of the values to be formatted (one of the arguments objects).
For example:
(format "The value of fill-column is %d." fill-column)
⇒ "The value of fill-column is 72."
Since format interprets ‘%’ characters as format
specifications, you should never pass an arbitrary string as
the first argument. This is particularly true when the string is
generated by some Lisp code. Unless the string is known to
never include any ‘%’ characters, pass "%s", described
below, as the first argument, and the string as the second, like this:
(format "%s" arbitrary-string)
If string contains more than one format specification, the format specifications correspond to successive values from objects. Thus, the first format specification in string uses the first such value, the second format specification uses the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause an error. Any extra values to be formatted are ignored.
Certain format specifications require values of particular types. If you supply a value that doesn't fit the requirements, an error is signaled.
Here is a table of valid format specifications:
princ, not
prin1—see Output Functions). Thus, strings are represented
by their contents alone, with no ‘"’ characters, and symbols appear
without ‘\’ characters.
If the object is a string, its text properties are
copied into the output. The text properties of the ‘%s’ itself
are also copied, but those of the object take priority.
prin1—see Output Functions). Thus, strings are enclosed in ‘"’ characters, and
‘\’ characters appear where necessary before special characters.
(format "%% %d" 30) returns "% 30".
Any other format character results in an ‘Invalid format operation’ error.
Here are several examples:
(format "The name of this buffer is %s." (buffer-name))
⇒ "The name of this buffer is strings.texi."
(format "The buffer object prints as %s." (current-buffer))
⇒ "The buffer object prints as strings.texi."
(format "The octal value of %d is %o,
and the hex value is %x." 18 18 18)
⇒ "The octal value of 18 is 22,
and the hex value is 12."
A specification can have a width, which is a decimal number
between the ‘%’ and the specification character. If the printed
representation of the object contains fewer characters than this
width, format extends it with padding. The width specifier is
ignored for the ‘%%’ specification. Any padding introduced by
the width specifier normally consists of spaces inserted on the left:
(format "%5d is padded on the left with spaces" 123)
⇒ " 123 is padded on the left with spaces"
If the width is too small, format does not truncate the
object's printed representation. Thus, you can use a width to specify
a minimum spacing between columns with no risk of losing information.
In the following three examples, ‘%7s’ specifies a minimum width
of 7. In the first case, the string inserted in place of ‘%7s’
has only 3 letters, and needs 4 blank spaces as padding. In the
second case, the string "specification" is 13 letters wide but
is not truncated.
(format "The word `%7s' actually has %d letters in it."
"foo" (length "foo"))
⇒ "The word ` foo' actually has 3 letters in it."
(format "The word `%7s' actually has %d letters in it."
"specification" (length "specification"))
⇒ "The word `specification' actually has 13 letters in it."
Immediately after the ‘%’ and before the optional width specifier, you can also put certain flag characters.
The flag ‘+’ inserts a plus sign before a positive number, so that it always has a sign. A space character as flag inserts a space before a positive number. (Otherwise, positive numbers start with the first digit.) These flags are useful for ensuring that positive numbers and negative numbers use the same number of columns. They are ignored except for ‘%d’, ‘%e’, ‘%f’, ‘%g’, and if both flags are used, ‘+’ takes precedence.
The flag ‘#’ specifies an “alternate form” which depends on the format in use. For ‘%o’, it ensures that the result begins with a ‘0’. For ‘%x’ and ‘%X’, it prefixes the result with ‘0x’ or ‘0X’. For ‘%e’, ‘%f’, and ‘%g’, the ‘#’ flag means include a decimal point even if the precision is zero.
The flag ‘-’ causes the padding inserted by the width specifier, if any, to be inserted on the right rather than the left. The flag ‘0’ ensures that the padding consists of ‘0’ characters instead of spaces, inserted on the left. These flags are ignored for specification characters for which they do not make sense: ‘%s’, ‘%S’ and ‘%c’ accept the ‘0’ flag, but still pad with spaces on the left. If both ‘-’ and ‘0’ are present and valid, ‘-’ takes precedence.
(format "%06d is padded on the left with zeros" 123)
⇒ "000123 is padded on the left with zeros"
(format "%-6d is padded on the right" 123)
⇒ "123 is padded on the right"
(format "The word `%-7s' actually has %d letters in it."
"foo" (length "foo"))
⇒ "The word `foo ' actually has 3 letters in it."
All the specification characters allow an optional precision before the character (after the width, if present). The precision is a decimal-point ‘.’ followed by a digit-string. For the floating-point specifications (‘%e’, ‘%f’, ‘%g’), the precision specifies how many decimal places to show; if zero, the decimal-point itself is also omitted. For ‘%s’ and ‘%S’, the precision truncates the string to the given width, so ‘%.3s’ shows only the first three characters of the representation for object. Precision has no effect for other specification characters.
The character case functions change the case of single characters or of the contents of strings. The functions normally convert only alphabetic characters (the letters ‘A’ through ‘Z’ and ‘a’ through ‘z’, as well as non-ASCII letters); other characters are not altered. You can specify a different case conversion mapping by specifying a case table (see Case Tables).
These functions do not modify the strings that are passed to them as arguments.
The examples below use the characters ‘X’ and ‘x’ which have ASCII codes 88 and 120 respectively.
This function converts string-or-char, which should be either a character or a string, to lower case.
When string-or-char is a string, this function returns a new string in which each letter in the argument that is upper case is converted to lower case. When string-or-char is a character, this function returns the corresponding lower case character (an integer); if the original character is lower case, or is not a letter, the return value is equal to the original character.
(downcase "The cat in the hat") ⇒ "the cat in the hat" (downcase ?X) ⇒ 120
This function converts string-or-char, which should be either a character or a string, to upper case.
When string-or-char is a string, this function returns a new string in which each letter in the argument that is lower case is converted to upper case. When string-or-char is a character, this function returns the corresponding upper case character (an integer); if the original character is upper case, or is not a letter, the return value is equal to the original character.
(upcase "The cat in the hat") ⇒ "THE CAT IN THE HAT" (upcase ?x) ⇒ 88
This function capitalizes strings or characters. If string-or-char is a string, the function returns a new string whose contents are a copy of string-or-char in which each word has been capitalized. This means that the first character of each word is converted to upper case, and the rest are converted to lower case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (see Syntax Class Table).
When string-or-char is a character, this function does the same thing as
upcase.(capitalize "The cat in the hat") ⇒ "The Cat In The Hat" (capitalize "THE 77TH-HATTED CAT") ⇒ "The 77th-Hatted Cat" (capitalize ?x) ⇒ 88
If string-or-char is a string, this function capitalizes the initials of the words in string-or-char, without altering any letters other than the initials. It returns a new string whose contents are a copy of string-or-char, in which each word has had its initial letter converted to upper case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (see Syntax Class Table).
When the argument to
upcase-initialsis a character,upcase-initialshas the same result asupcase.(upcase-initials "The CAT in the hAt") ⇒ "The CAT In The HAt"
See Text Comparison, for functions that compare strings; some of them ignore case differences, or can optionally ignore case differences.
You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the case conversion functions for Lisp objects (see the previous section) and those that apply to text in the buffer (see Case Changes). Each buffer has a case table; there is also a standard case table which is used to initialize the case table of new buffers.
A case table is a char-table (see Char-Tables) whose subtype is
case-table. This char-table maps each character into the
corresponding lower case character. It has three extra slots, which
hold related tables:
In simple cases, all you need to specify is the mapping to lower-case; the three related tables will be calculated automatically from that one.
For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both lower case and upper case.
The extra table canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character. For example, since ‘a’ and ‘A’ are related by case-conversion, they should have the same canonical equivalent character (which should be either ‘a’ for both of them, or ‘A’ for both of them).
The extra table equivalences is a map that cyclically permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ASCII, this would map ‘a’ into ‘A’ and ‘A’ into ‘a’, and likewise for each set of equivalent characters.)
When constructing a case table, you can provide nil for
canonicalize; then Emacs fills in this slot from the lower case
and upper case mappings. You can also provide nil for
equivalences; then Emacs fills in this slot from
canonicalize. In a case table that is actually in use, those
components are non-nil. Do not try to specify
equivalences without also specifying canonicalize.
Here are the functions for working with case tables:
This function makes table the standard case table, so that it will be used in any buffers created subsequently.
The
with-case-tablemacro saves the current case table, makes table the current case table, evaluates the body forms, and finally restores the case table. The return value is the value of the last form in body. The case table is restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).
Some language environments modify the case conversions of
ASCII characters; for example, in the Turkish language
environment, the ASCII character ‘I’ is downcased into
a Turkish “dotless i”. This can interfere with code that requires
ordinary ASCII case conversion, such as implementations of
ASCII-based network protocols. In that case, use the
with-case-table macro with the variable ascii-case-table,
which stores the unmodified case table for the ASCII
character set.
The case table for the ASCII character set. This should not be modified by any language environment settings.
The following three functions are convenient subroutines for packages that define non-ASCII character sets. They modify the specified case table case-table; they also modify the standard syntax table. See Syntax Tables. Normally you would use these functions to change the standard case table.
This function specifies a pair of corresponding letters, one upper case and one lower case.
This function makes characters l and r a matching pair of case-invariant delimiters.
This function makes char case-invariant, with syntax syntax.
This command displays a description of the contents of the current buffer's case table.
A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list.
Lists in Lisp are not a primitive data type; they are built up from cons cells. A cons cell is a data object that represents an ordered pair. That is, it has two slots, and each slot holds, or refers to, some Lisp object. One slot is known as the car, and the other is known as the cdr. (These names are traditional; see Cons Cell类型.) cdr is pronounced “could-er.”
We say that “the car of this cons cell is” whatever object its car slot currently holds, and likewise for the cdr.
A list is a series of cons cells “chained together,” so that each
cell refers to the next one. There is one cons cell for each element of
the list. By convention, the cars of the cons cells hold the
elements of the list, and the cdrs are used to chain the list: the
cdr slot of each cons cell refers to the following cons cell. The
cdr of the last cons cell is nil. This asymmetry between
the car and the cdr is entirely a matter of convention; at the
level of cons cells, the car and cdr slots have the same
characteristics.
Since nil is the conventional value to put in the cdr of
the last cons cell in the list, we call that case a true list.
In Lisp, we consider the symbol nil a list as well as a
symbol; it is the list with no elements. For convenience, the symbol
nil is considered to have nil as its cdr (and also
as its car). Therefore, the cdr of a true list is always a
true list.
If the cdr of a list's last cons cell is some other value,
neither nil nor another cons cell, we call the structure a
dotted list, since its printed representation would use
‘.’. There is one other possibility: some cons cell's cdr
could point to one of the previous cons cells in the list. We call
that structure a circular list.
For some purposes, it does not matter whether a list is true, circular or dotted. If the program doesn't look far enough down the list to see the cdr of the final cons cell, it won't care. However, some functions that operate on lists demand true lists and signal errors if given a dotted list. Most functions that try to find the end of a list enter infinite loops if given a circular list.
Because most cons cells are used as part of lists, the phrase list structure has come to mean any structure made out of cons cells.
The cdr of any nonempty true list l is a list containing all the elements of l except the first.
See Cons Cell类型, for the read and print syntax of cons cells and lists, and for “box and arrow” illustrations of lists.
The following predicates test whether a Lisp object is an atom,
whether it is a cons cell or is a list, or whether it is the
distinguished object nil. (Many of these predicates can be
defined in terms of the others, but they are used so often that it is
worth having all of them.)
This function returns
tif object is a cons cell,nilotherwise.nilis not a cons cell, although it is a list.
This function returns
tif object is an atom,nilotherwise. All objects except cons cells are atoms. The symbolnilis an atom and is also a list; it is the only Lisp object that is both.(atom object) == (not (consp object))
This function returns
tif object is a cons cell ornil. Otherwise, it returnsnil.(listp '(1)) ⇒ t (listp '()) ⇒ t
This function is the opposite of
listp: it returnstif object is not a list. Otherwise, it returnsnil.(listp object) == (not (nlistp object))
This function returns
tif object isnil, and returnsnilotherwise. This function is identical tonot, but as a matter of clarity we usenullwhen object is considered a list andnotwhen it is considered a truth value (seenotin Combining Conditions).(null '(1)) ⇒ nil (null '()) ⇒ t
This function returns the value referred to by the first slot of the cons cell cons-cell. In other words, it returns the car of cons-cell.
As a special case, if cons-cell is
nil, this function returnsnil. Therefore, any list is a valid argument. An error is signaled if the argument is not a cons cell ornil.(car '(a b c)) ⇒ a (car '()) ⇒ nil
This function returns the value referred to by the second slot of the cons cell cons-cell. In other words, it returns the cdr of cons-cell.
As a special case, if cons-cell is
nil, this function returnsnil; therefore, any list is a valid argument. An error is signaled if the argument is not a cons cell ornil.(cdr '(a b c)) ⇒ (b c) (cdr '()) ⇒ nil
This function lets you take the car of a cons cell while avoiding errors for other data types. It returns the car of object if object is a cons cell,
nilotherwise. This is in contrast tocar, which signals an error if object is not a list.(car-safe object) == (let ((x object)) (if (consp x) (car x) nil))
This function lets you take the cdr of a cons cell while avoiding errors for other data types. It returns the cdr of object if object is a cons cell,
nilotherwise. This is in contrast tocdr, which signals an error if object is not a list.(cdr-safe object) == (let ((x object)) (if (consp x) (cdr x) nil))
This macro is a way of examining the car of a list, and taking it off the list, all at once.
It operates on the list which is stored in the symbol listname. It removes this element from the list by setting listname to the cdr of its old value—but it also returns the car of that list, which is the element being removed.
x ⇒ (a b c) (pop x) ⇒ a x ⇒ (b c)
This function returns the nth element of list. Elements are numbered starting with zero, so the car of list is element number zero. If the length of list is n or less, the value is
nil.If n is negative,
nthreturns the first element of list.(nth 2 '(1 2 3 4)) ⇒ 3 (nth 10 '(1 2 3 4)) ⇒ nil (nth -3 '(1 2 3 4)) ⇒ 1 (nth n x) == (car (nthcdr n x))The function
eltis similar, but applies to any kind of sequence. For historical reasons, it takes its arguments in the opposite order. See Sequence Functions.
This function returns the nth cdr of list. In other words, it skips past the first n links of list and returns what follows.
If n is zero or negative,
nthcdrreturns all of list. If the length of list is n or less,nthcdrreturnsnil.(nthcdr 1 '(1 2 3 4)) ⇒ (2 3 4) (nthcdr 10 '(1 2 3 4)) ⇒ nil (nthcdr -3 '(1 2 3 4)) ⇒ (1 2 3 4)
This function returns the last link of list. The
carof this link is the list's last element. If list is null,nilis returned. If n is non-nil, the nth-to-last link is returned instead, or the whole of list if n is bigger than list's length.
This function returns the length of list, with no risk of either an error or an infinite loop. It generally returns the number of distinct cons cells in the list. However, for circular lists, the value is just an upper bound; it is often too large.
If list is not
nilor a cons cell,safe-lengthreturns 0.
The most common way to compute the length of a list, when you are not
worried that it may be circular, is with length. See Sequence Functions.
This function returns the list x with the last element, or the last n elements, removed. If n is greater than zero it makes a copy of the list so as not to damage the original list. In general,
(append (butlastx n) (lastx n))will return a list equal to x.
This is a version of
butlastthat works by destructively modifying thecdrof the appropriate element, rather than making a copy of the list.
Many functions build lists, as lists reside at the very heart of Lisp.
cons is the fundamental list-building function; however, it is
interesting to note that list is used more times in the source
code for Emacs than cons.
This function is the most basic function for building new list structure. It creates a new cons cell, making object1 the car, and object2 the cdr. It then returns the new cons cell. The arguments object1 and object2 may be any Lisp objects, but most often object2 is a list.
(cons 1 '(2)) ⇒ (1 2) (cons 1 '()) ⇒ (1) (cons 1 2) ⇒ (1 . 2)
consis often used to add a single element to the front of a list. This is called consing the element onto the list. 1 For example:(setq list (cons newelt list))Note that there is no conflict between the variable named
listused in this example and the function namedlistdescribed below; any symbol can serve both purposes.
This function creates a list with objects as its elements. The resulting list is always
nil-terminated. If no objects are given, the empty list is returned.(list 1 2 3 4 5) ⇒ (1 2 3 4 5) (list 1 2 '(3 4 5) 'foo) ⇒ (1 2 (3 4 5) foo) (list) ⇒ nil
This function creates a list of length elements, in which each element is object. Compare
make-listwithmake-string(see Creating Strings).(make-list 3 'pigs) ⇒ (pigs pigs pigs) (make-list 0 'pigs) ⇒ nil (setq l (make-list 3 '(a b)) ⇒ ((a b) (a b) (a b)) (eq (car l) (cadr l)) ⇒ t
This function returns a list containing all the elements of sequences. The sequences may be lists, vectors, bool-vectors, or strings, but the last one should usually be a list. All arguments except the last one are copied, so none of the arguments is altered. (See
nconcin Rearrangement, for a way to join lists with no copying.)More generally, the final argument to
appendmay be any Lisp object. The final argument is not copied or converted; it becomes the cdr of the last cons cell in the new list. If the final argument is itself a list, then its elements become in effect elements of the result list. If the final element is not a list, the result is a dotted list since its final cdr is notnilas required in a true list.
Here is an example of using append:
(setq trees '(pine oak))
⇒ (pine oak)
(setq more-trees (append '(maple birch) trees))
⇒ (maple birch pine oak)
trees
⇒ (pine oak)
more-trees
⇒ (maple birch pine oak)
(eq trees (cdr (cdr more-trees)))
⇒ t
You can see how append works by looking at a box diagram. The
variable trees is set to the list (pine oak) and then the
variable more-trees is set to the list (maple birch pine
oak). However, the variable trees continues to refer to the
original list:
more-trees trees
| |
| --- --- --- --- -> --- --- --- ---
--> | | |--> | | |--> | | |--> | | |--> nil
--- --- --- --- --- --- --- ---
| | | |
| | | |
--> maple -->birch --> pine --> oak
An empty sequence contributes nothing to the value returned by
append. As a consequence of this, a final nil argument
forces a copy of the previous argument:
trees
⇒ (pine oak)
(setq wood (append trees nil))
⇒ (pine oak)
wood
⇒ (pine oak)
(eq wood trees)
⇒ nil
This once was the usual way to copy a list, before the function
copy-sequence was invented. See Sequences Arrays Vectors.
Here we show the use of vectors and strings as arguments to append:
(append [a b] "cd" nil)
⇒ (a b 99 100)
With the help of apply (see Calling Functions), we can append
all the lists in a list of lists:
(apply 'append '((a b c) nil (x y z) nil))
⇒ (a b c x y z)
If no sequences are given, nil is returned:
(append)
⇒ nil
Here are some examples where the final argument is not a list:
(append '(x y) 'z)
⇒ (x y . z)
(append '(x y) [z])
⇒ (x y . [z])
The second example shows that when the final argument is a sequence but not a list, the sequence's elements do not become elements of the resulting list. Instead, the sequence becomes the final cdr, like any other non-list final argument.
This function creates a new list whose elements are the elements of list, but in reverse order. The original argument list is not altered.
(setq x '(1 2 3 4)) ⇒ (1 2 3 4) (reverse x) ⇒ (4 3 2 1) x ⇒ (1 2 3 4)
This function returns a copy of the tree
tree. If tree is a cons cell, this makes a new cons cell with the same car and cdr, then recursively copies the car and cdr in the same way.Normally, when tree is anything other than a cons cell,
copy-treesimply returns tree. However, if vecp is non-nil, it copies vectors too (and operates recursively on their elements).
This returns a list of numbers starting with from and incrementing by separation, and ending at or just before to. separation can be positive or negative and defaults to 1. If to is
nilor numerically equal to from, the value is the one-element list(from). If to is less than from with a positive separation, or greater than from with a negative separation, the value isnilbecause those arguments specify an empty sequence.If separation is 0 and to is neither
nilnor numerically equal to from,number-sequencesignals an error, since those arguments specify an infinite sequence.All arguments can be integers or floating point numbers. However, floating point arguments can be tricky, because floating point arithmetic is inexact. For instance, depending on the machine, it may quite well happen that
(number-sequence 0.4 0.6 0.2)returns the one element list(0.4), whereas(number-sequence 0.4 0.8 0.2)returns a list with three elements. The nth element of the list is computed by the exact formula(+from(*n separation)). Thus, if one wants to make sure that to is included in the list, one can pass an expression of this exact type for to. Alternatively, one can replace to with a slightly larger value (or a slightly more negative value if separation is negative).Some examples:
(number-sequence 4 9) ⇒ (4 5 6 7 8 9) (number-sequence 9 4 -1) ⇒ (9 8 7 6 5 4) (number-sequence 9 4 -2) ⇒ (9 7 5) (number-sequence 8) ⇒ (8) (number-sequence 8 5) ⇒ nil (number-sequence 5 8 -1) ⇒ nil (number-sequence 1.5 6 2) ⇒ (1.5 3.5 5.5)
These functions, and one macro, provide convenient ways to modify a list which is stored in a variable.
This macro provides an alternative way to write
(setqlistname(consnewelt listname)).(setq l '(a b)) ⇒ (a b) (push 'c l) ⇒ (c a b) l ⇒ (c a b)
Two functions modify lists that are the values of variables.
This function sets the variable symbol by consing element onto the old value, if element is not already a member of that value. It returns the resulting list, whether updated or not. The value of symbol had better be a list already before the call.
add-to-listuses compare-fn to compare element against existing list members; if compare-fn isnil, it usesequal.Normally, if element is added, it is added to the front of symbol, but if the optional argument append is non-
nil, it is added at the end.The argument symbol is not implicitly quoted;
add-to-listis an ordinary function, likesetand unlikesetq. Quote the argument yourself if that is what you want.
Here's a scenario showing how to use add-to-list:
(setq foo '(a b))
⇒ (a b)
(add-to-list 'foo 'c) ;; Add c.
⇒ (c a b)
(add-to-list 'foo 'b) ;; No effect.
⇒ (c a b)
foo ;; foo was changed.
⇒ (c a b)
An equivalent expression for (add-to-list 'var
value) is this:
(or (member value var)
(setq var (cons value var)))
This function sets the variable symbol by inserting element into the old value, which must be a list, at the position specified by order. If element is already a member of the list, its position in the list is adjusted according to order. Membership is tested using
eq. This function returns the resulting list, whether updated or not.The order is typically a number (integer or float), and the elements of the list are sorted in non-decreasing numerical order.
order may also be omitted or
nil. Then the numeric order of element stays unchanged if it already has one; otherwise, element has no numeric order. Elements without a numeric list order are placed at the end of the list, in no particular order.Any other value for order removes the numeric order of element if it already has one; otherwise, it is equivalent to
nil.The argument symbol is not implicitly quoted;
add-to-ordered-listis an ordinary function, likesetand unlikesetq. Quote the argument yourself if that is what you want.The ordering information is stored in a hash table on symbol's
list-orderproperty.
Here's a scenario showing how to use add-to-ordered-list:
(setq foo '())
⇒ nil
(add-to-ordered-list 'foo 'a 1) ;; Add a.
⇒ (a)
(add-to-ordered-list 'foo 'c 3) ;; Add c.
⇒ (a c)
(add-to-ordered-list 'foo 'b 2) ;; Add b.
⇒ (a b c)
(add-to-ordered-list 'foo 'b 4) ;; Move b.
⇒ (a c b)
(add-to-ordered-list 'foo 'd) ;; Append d.
⇒ (a c b d)
(add-to-ordered-list 'foo 'e) ;; Add e.
⇒ (a c b e d)
foo ;; foo was changed.
⇒ (a c b e d)
You can modify the car and cdr contents of a cons cell with the
primitives setcar and setcdr. We call these “destructive”
operations because they change existing list structure.
Common Lisp note: Common Lisp uses functionsrplacaandrplacdto alter list structure; they change structure the same way assetcarandsetcdr, but the Common Lisp functions return the cons cell whilesetcarandsetcdrreturn the new car or cdr.
setcarChanging the car of a cons cell is done with setcar. When
used on a list, setcar replaces one element of a list with a
different element.
This function stores object as the new car of cons, replacing its previous car. In other words, it changes the car slot of cons to refer to object. It returns the value object. For example:
(setq x '(1 2)) ⇒ (1 2) (setcar x 4) ⇒ 4 x ⇒ (4 2)
When a cons cell is part of the shared structure of several lists, storing a new car into the cons changes one element of each of these lists. Here is an example:
;; Create two lists that are partly shared. (setq x1 '(a b c)) ⇒ (a b c) (setq x2 (cons 'z (cdr x1))) ⇒ (z b c) ;; Replace the car of a shared link. (setcar (cdr x1) 'foo) ⇒ foo x1 ; Both lists are changed. ⇒ (a foo c) x2 ⇒ (z foo c) ;; Replace the car of a link that is not shared. (setcar x1 'baz) ⇒ baz x1 ; Only one list is changed. ⇒ (baz foo c) x2 ⇒ (z foo c)
Here is a graphical depiction of the shared structure of the two lists
in the variables x1 and x2, showing why replacing b
changes them both:
--- --- --- --- --- ---
x1---> | | |----> | | |--> | | |--> nil
--- --- --- --- --- ---
| --> | |
| | | |
--> a | --> b --> c
|
--- --- |
x2--> | | |--
--- ---
|
|
--> z
Here is an alternative form of box diagram, showing the same relationship:
x1:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| a | o------->| b | o------->| c | nil |
| | | -->| | | | | |
-------------- | -------------- --------------
|
x2: |
-------------- |
| car | cdr | |
| z | o----
| | |
--------------
The lowest-level primitive for modifying a cdr is setcdr:
This function stores object as the new cdr of cons, replacing its previous cdr. In other words, it changes the cdr slot of cons to refer to object. It returns the value object.
Here is an example of replacing the cdr of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the car of the list, and is not reached via the cdr.
(setq x '(1 2 3))
⇒ (1 2 3)
(setcdr x '(4))
⇒ (4)
x
⇒ (1 4)
You can delete elements from the middle of a list by altering the
cdrs of the cons cells in the list. For example, here we delete
the second element, b, from the list (a b c), by changing
the cdr of the first cons cell:
(setq x1 '(a b c))
⇒ (a b c)
(setcdr x1 (cdr (cdr x1)))
⇒ (c)
x1
⇒ (a c)
Here is the result in box notation:
--------------------
| |
-------------- | -------------- | --------------
| car | cdr | | | car | cdr | -->| car | cdr |
| a | o----- | b | o-------->| c | nil |
| | | | | | | | |
-------------- -------------- --------------
The second cons cell, which previously held the element b, still
exists and its car is still b, but it no longer forms part
of this list.
It is equally easy to insert a new element by changing cdrs:
(setq x1 '(a b c))
⇒ (a b c)
(setcdr x1 (cons 'd (cdr x1)))
⇒ (d b c)
x1
⇒ (a d b c)
Here is this result in box notation:
-------------- ------------- -------------
| car | cdr | | car | cdr | | car | cdr |
| a | o | -->| b | o------->| c | nil |
| | | | | | | | | | |
--------- | -- | ------------- -------------
| |
----- --------
| |
| --------------- |
| | car | cdr | |
-->| d | o------
| | |
---------------
Here are some functions that rearrange lists “destructively” by modifying the cdrs of their component cons cells. We call these functions “destructive” because they chew up the original lists passed to them as arguments, relinking their cons cells to form a new list that is the returned value.
See delq, in Sets And Lists, for another function
that modifies cons cells.
This function returns a list containing all the elements of lists. Unlike
append(see Building Lists), the lists are not copied. Instead, the last cdr of each of the lists is changed to refer to the following list. The last of the lists is not altered. For example:(setq x '(1 2 3)) ⇒ (1 2 3) (nconc x '(4 5)) ⇒ (1 2 3 4 5) x ⇒ (1 2 3 4 5)Since the last argument of
nconcis not itself modified, it is reasonable to use a constant list, such as'(4 5), as in the above example. For the same reason, the last argument need not be a list:(setq x '(1 2 3)) ⇒ (1 2 3) (nconc x 'z) ⇒ (1 2 3 . z) x ⇒ (1 2 3 . z)However, the other arguments (all but the last) must be lists.
A common pitfall is to use a quoted constant list as a non-last argument to
nconc. If you do this, your program will change each time you run it! Here is what happens:(defun add-foo (x) ; We want this function to add (nconc '(foo) x)) ;footo the front of its arg. (symbol-function 'add-foo) ⇒ (lambda (x) (nconc (quote (foo)) x)) (setq xx (add-foo '(1 2))) ; It seems to work. ⇒ (foo 1 2) (setq xy (add-foo '(3 4))) ; What happened? ⇒ (foo 1 2 3 4) (eq xx xy) ⇒ t (symbol-function 'add-foo) ⇒ (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
This function reverses the order of the elements of list. Unlike
reverse,nreversealters its argument by reversing the cdrs in the cons cells forming the list. The cons cell that used to be the last one in list becomes the first cons cell of the value.For example:
(setq x '(a b c)) ⇒ (a b c) x ⇒ (a b c) (nreverse x) ⇒ (c b a) ;; The cons cell that was first is now last. x ⇒ (a)To avoid confusion, we usually store the result of
nreverseback in the same variable which held the original list:(setq x (nreverse x))Here is the
nreverseof our favorite example,(a b c), presented graphically:Original list head: Reversed list: ------------- ------------- ------------ | car | cdr | | car | cdr | | car | cdr | | a | nil |<-- | b | o |<-- | c | o | | | | | | | | | | | | | | ------------- | --------- | - | -------- | - | | | | ------------- ------------
This function sorts list stably, though destructively, and returns the sorted list. It compares elements using predicate. A stable sort is one in which elements with equal sort keys maintain their relative order before and after the sort. Stability is important when successive sorts are used to order elements according to different criteria.
The argument predicate must be a function that accepts two arguments. It is called with two elements of list. To get an increasing order sort, the predicate should return non-
nilif the first element is “less than” the second, ornilif not.The comparison function predicate must give reliable results for any given pair of arguments, at least within a single call to
sort. It must be antisymmetric; that is, if a is less than b, b must not be less than a. It must be transitive—that is, if a is less than b, and b is less than c, then a must be less than c. If you use a comparison function which does not meet these requirements, the result ofsortis unpredictable.The destructive aspect of
sortis that it rearranges the cons cells forming list by changing cdrs. A nondestructive sort function would create new cons cells to store the elements in their sorted order. If you wish to make a sorted copy without destroying the original, copy it first withcopy-sequenceand then sort.Sorting does not change the cars of the cons cells in list; the cons cell that originally contained the element
ain list still hasain its car after sorting, but it now appears in a different position in the list due to the change of cdrs. For example:(setq nums '(1 3 2 6 5 4 0)) ⇒ (1 3 2 6 5 4 0) (sort nums '<) ⇒ (0 1 2 3 4 5 6) nums ⇒ (1 2 3 4 5 6)Warning: Note that the list in
numsno longer contains 0; this is the same cons cell that it was before, but it is no longer the first one in the list. Don't assume a variable that formerly held the argument now holds the entire sorted list! Instead, save the result ofsortand use that. Most often we store the result back into the variable that held the original list:(setq nums (sort nums '<))See Sorting, for more functions that perform sorting. See
documentationin Accessing Documentation, for a useful example ofsort.
A list can represent an unordered mathematical set—simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list. To form the union of two sets, use append (as
long as you don't mind having duplicate elements). You can remove
equal duplicates using delete-dups. Other useful
functions for sets include memq and delq, and their
equal versions, member and delete.
Common Lisp note: Common Lisp has functionsunion(which avoids duplicate elements) andintersectionfor set operations, but GNU Emacs Lisp does not have them. You can write them in Lisp if you wish.
This function tests to see whether object is a member of list. If it is,
memqreturns a list starting with the first occurrence of object. Otherwise, it returnsnil. The letter ‘q’ inmemqsays that it useseqto compare object against the elements of the list. For example:(memq 'b '(a b c b a)) ⇒ (b c b a) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. ⇒ nil
This function destructively removes all elements
eqto object from list. The letter ‘q’ indelqsays that it useseqto compare object against the elements of the list, likememqandremq.
When delq deletes elements from the front of the list, it does so
simply by advancing down the list and returning a sublist that starts
after those elements:
(delq 'a '(a b c)) == (cdr '(a b c))
When an element to be deleted appears in the middle of the list, removing it involves changing the cdrs (see Setcdr).
(setq sample-list '(a b c (4)))
⇒ (a b c (4))
(delq 'a sample-list)
⇒ (b c (4))
sample-list
⇒ (a b c (4))
(delq 'c sample-list)
⇒ (a b (4))
sample-list
⇒ (a b (4))
Note that (delq 'c sample-list) modifies sample-list to
splice out the third element, but (delq 'a sample-list) does not
splice anything—it just returns a shorter list. Don't assume that a
variable which formerly held the argument list now has fewer
elements, or that it still holds the original list! Instead, save the
result of delq and use that. Most often we store the result back
into the variable that held the original list:
(setq flowers (delq 'rose flowers))
In the following example, the (4) that delq attempts to match
and the (4) in the sample-list are not eq:
(delq '(4) sample-list)
⇒ (a c (4))
If you want to delete elements that are equal to a given value,
use delete (see below).
This function returns a copy of list, with all elements removed which are
eqto object. The letter ‘q’ inremqsays that it useseqto compare object against the elements oflist.(setq sample-list '(a b c a b c)) ⇒ (a b c a b c) (remq 'a sample-list) ⇒ (b c b c) sample-list ⇒ (a b c a b c)
The function
memqltests to see whether object is a member of list, comparing members with object usingeql, so floating point elements are compared by value. If object is a member,memqlreturns a list starting with its first occurrence in list. Otherwise, it returnsnil.Compare this with
memq:(memql 1.2 '(1.1 1.2 1.3)) ;1.2and1.2areeql. ⇒ (1.2 1.3) (memq 1.2 '(1.1 1.2 1.3)) ;1.2and1.2are noteq. ⇒ nil
The following three functions are like memq, delq and
remq, but use equal rather than eq to compare
elements. See 相等判定.
The function
membertests to see whether object is a member of list, comparing members with object usingequal. If object is a member,memberreturns a list starting with its first occurrence in list. Otherwise, it returnsnil.Compare this with
memq:(member '(2) '((1) (2))) ;(2)and(2)areequal. ⇒ ((2)) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. ⇒ nil ;; Two strings with the same contents areequal. (member "foo" '("foo" "bar")) ⇒ ("foo" "bar")
If
sequenceis a list, this function destructively removes all elementsequalto object from sequence. For lists,deleteis todelqasmemberis tomemq: it usesequalto compare elements with object, likemember; when it finds an element that matches, it cuts the element out just asdelqwould.If
sequenceis a vector or string,deletereturns a copy ofsequencewith all elementsequaltoobjectremoved.For example:
(setq l '((2) (1) (2))) (delete '(2) l) ⇒ ((1)) l ⇒ ((2) (1)) ;; If you want to changelreliably, ;; write(setq l (delete elt l)). (setq l '((2) (1) (2))) (delete '(1) l) ⇒ ((2) (2)) l ⇒ ((2) (2)) ;; In this case, it makes no difference whether you setl, ;; but you should do so for the sake of the other case. (delete '(2) [(2) (1) (2)]) ⇒ [(1)]
This function is the non-destructive counterpart of
delete. It returns a copy ofsequence, a list, vector, or string, with elementsequaltoobjectremoved. For example:(remove '(2) '((2) (1) (2))) ⇒ ((1)) (remove '(2) [(2) (1) (2)]) ⇒ [(1)]
Common Lisp note: The functionsmember,deleteandremovein GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not useequalto compare elements.
This function is like
member, except that object should be a string and that it ignores differences in letter-case and text representation: upper-case and lower-case letters are treated as equal, and unibyte strings are converted to multibyte prior to comparison.
This function destructively removes all
equalduplicates from list, stores the result in list and returns it. Of severalequaloccurrences of an element in list,delete-dupskeeps the first one.
See also the function add-to-list, in List Variables,
for a way to add an element to a list stored in a variable and used as a
set.
An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the car of each cons cell is the key, and the cdr is the associated value.2
Here is an example of an alist. The key pine is associated with
the value cones; the key oak is associated with
acorns; and the key maple is associated with seeds.
((pine . cones)
(oak . acorns)
(maple . seeds))
Both the values and the keys in an alist may be any Lisp objects.
For example, in the following alist, the symbol a is
associated with the number 1, and the string "b" is
associated with the list (2 3), which is the cdr of
the alist element:
((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated value in the car of the cdr of the element. Here is an example of such an alist:
((rose red) (lily white) (buttercup yellow))
Here we regard red as the value associated with rose. One
advantage of this kind of alist is that you can store other related
information—even a list of other items—in the cdr of the
cdr. One disadvantage is that you cannot use rassq (see
below) to find the element containing a given value. When neither of
these considerations is important, the choice is a matter of taste, as
long as you are consistent about it for any given alist.
The same alist shown above could be regarded as having the
associated value in the cdr of the element; the value associated
with rose would be the list (red).
Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one.
In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases.
Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See Property Lists, for a comparison of property lists and association lists.
This function returns the first association for key in alist, comparing key against the alist elements using
equal(see 相等判定). It returnsnilif no association in alist has a carequalto key. For example:(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) ⇒ ((pine . cones) (oak . acorns) (maple . seeds)) (assoc 'oak trees) ⇒ (oak . acorns) (cdr (assoc 'oak trees)) ⇒ acorns (assoc 'birch trees) ⇒ nilHere is another example, in which the keys and values are not symbols:
(setq needles-per-cluster '((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine"))) (cdr (assoc 3 needles-per-cluster)) ⇒ ("Pitch Pine") (cdr (assoc 2 needles-per-cluster)) ⇒ ("Austrian Pine" "Red Pine")
The function assoc-string is much like assoc except
that it ignores certain differences between strings. See Text Comparison.
This function returns the first association with value value in alist. It returns
nilif no association in alist has a cdrequalto value.
rassocis likeassocexcept that it compares the cdr of each alist association instead of the car. You can think of this as “reverseassoc,” finding the key for a given value.
This function is like
associn that it returns the first association for key in alist, but it makes the comparison usingeqinstead ofequal.assqreturnsnilif no association in alist has a careqto key. This function is used more often thanassoc, sinceeqis faster thanequaland most alists use symbols as keys. See 相等判定.(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) ⇒ ((pine . cones) (oak . acorns) (maple . seeds)) (assq 'pine trees) ⇒ (pine . cones)On the other hand,
assqis not usually useful in alists where the keys may not be symbols:(setq leaves '(("simple leaves" . oak) ("compound leaves" . horsechestnut))) (assq "simple leaves" leaves) ⇒ nil (assoc "simple leaves" leaves) ⇒ ("simple leaves" . oak)
This function returns the first association with value value in alist. It returns
nilif no association in alist has a cdreqto value.
rassqis likeassqexcept that it compares the cdr of each alist association instead of the car. You can think of this as “reverseassq,” finding the key for a given value.For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) (rassq 'acorns trees) ⇒ (oak . acorns) (rassq 'spores trees) ⇒ nil
rassqcannot search for a value stored in the car of the cdr of an element:(setq colors '((rose red) (lily white) (buttercup yellow))) (rassq 'white colors) ⇒ nilIn this case, the cdr of the association
(lily white)is not the symbolwhite, but rather the list(white). This becomes clearer if the association is written in dotted pair notation:(lily white) == (lily . (white))
This function searches alist for a match for key. For each element of alist, it compares the element (if it is an atom) or the element's car (if it is a cons) against key, by calling test with two arguments: the element or its car, and key. The arguments are passed in that order so that you can get useful results using
string-matchwith an alist that contains regular expressions (see Regexp Search). If test is omitted ornil,equalis used for comparison.If an alist element matches key by this criterion, then
assoc-defaultreturns a value based on this element. If the element is a cons, then the value is the element's cdr. Otherwise, the return value is default.If no alist element matches key,
assoc-defaultreturnsnil.
This function returns a two-level deep copy of alist: it creates a new copy of each association, so that you can alter the associations of the new alist without changing the old one.
(setq needles-per-cluster '((2 . ("Austrian Pine" "Red Pine")) (3 . ("Pitch Pine")) (5 . ("White Pine")))) ⇒ ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (setq copy (copy-alist needles-per-cluster)) ⇒ ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (eq needles-per-cluster copy) ⇒ nil (equal needles-per-cluster copy) ⇒ t (eq (car needles-per-cluster) (car copy)) ⇒ nil (cdr (car (cdr needles-per-cluster))) ⇒ ("Pitch Pine") (eq (cdr (car (cdr needles-per-cluster))) (cdr (car (cdr copy)))) ⇒ tThis example shows how
copy-alistmakes it possible to change the associations of one copy without affecting the other:(setcdr (assq 3 copy) '("Martian Vacuum Pine")) (cdr (assq 3 needles-per-cluster)) ⇒ ("Pitch Pine")
This function deletes from alist all the elements whose car is
eqto key, much as if you useddelqto delete each such element one by one. It returns the shortened alist, and often modifies the original list structure of alist. For correct results, use the return value ofassq-delete-allrather than looking at the saved value of alist.(setq alist '((foo 1) (bar 2) (foo 3) (lose 4))) ⇒ ((foo 1) (bar 2) (foo 3) (lose 4)) (assq-delete-all 'foo alist) ⇒ ((bar 2) (lose 4)) alist ⇒ ((foo 1) (bar 2) (lose 4))
This function deletes from alist all the elements whose cdr is
eqto value. It returns the shortened alist, and often modifies the original list structure of alist.rassq-delete-allis likeassq-delete-allexcept that it compares the cdr of each alist association instead of the car.
This section describes functions for operating on rings. A ring is a fixed-size data structure that supports insertion, deletion, rotation, and modulo-indexed reference and traversal.
This returns a new ring capable of holding size objects. size should be an integer.
This returns the number of objects that ring currently contains. The value will never exceed that returned by
ring-size.
This returns a new ring which is a copy of ring. The new ring contains the same (
eq) objects as ring.
The newest element in the ring always has index 0. Higher indices correspond to older elements. Indices are computed modulo the ring length. Index −1 corresponds to the oldest element, −2 to the next-oldest, and so forth.
This returns the object in ring found at index index. index may be negative or greater than the ring length. If ring is empty,
ring-refsignals an error.
This inserts object into ring, making it the newest element, and returns object.
If the ring is full, insertion removes the oldest element to make room for the new element.
Remove an object from ring, and return that object. The argument index specifies which item to remove; if it is
nil, that means to remove the oldest item. If ring is empty,ring-removesignals an error.
This inserts object into ring, treating it as the oldest element. The return value is not significant.
If the ring is full, this function removes the newest element to make room for the inserted element.
If you are careful not to exceed the ring size, you can use the ring as a first-in-first-out queue. For example:
(let ((fifo (make-ring 5)))
(mapc (lambda (obj) (ring-insert fifo obj))
'(0 one "two"))
(list (ring-remove fifo) t
(ring-remove fifo) t
(ring-remove fifo)))
⇒ (0 t one t "two")
Recall that the sequence type is the union of two other Lisp types: lists and arrays. In other words, any list is a sequence, and any array is a sequence. The common property that all sequences have is that each is an ordered collection of elements.
An array is a fixed-length object with a slot for each of its elements. All the elements are accessible in constant time. The four types of arrays are strings, vectors, char-tables and bool-vectors.
A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Finding the nth element requires looking through n cons cells, so elements farther from the beginning of the list take longer to access. But it is possible to add elements to the list, or remove elements.
The following diagram shows the relationship between these types:
_____________________________________________
| |
| Sequence |
| ______ ________________________________ |
| | | | | |
| | List | | Array | |
| | | | ________ ________ | |
| |______| | | | | | | |
| | | Vector | | String | | |
| | |________| |________| | |
| | ____________ _____________ | |
| | | | | | | |
| | | Char-table | | Bool-vector | | |
| | |____________| |_____________| | |
| |________________________________| |
|_____________________________________________|
In Emacs Lisp, a sequence is either a list or an array. The common property of all sequences is that they are ordered collections of elements. This section describes functions that accept any kind of sequence.
Returns
tif object is a list, vector, string, bool-vector, or char-table,nilotherwise.
This function returns the number of elements in sequence. If sequence is a dotted list, a
wrong-type-argumenterror is signaled. Circular lists may cause an infinite loop. For a char-table, the value returned is always one more than the maximum Emacs character code.See Definition of safe-length, for the related function
safe-length.(length '(1 2 3)) ⇒ 3 (length ()) ⇒ 0 (length "foobar") ⇒ 6 (length [1 2 3]) ⇒ 3 (length (make-bool-vector 5 nil)) ⇒ 5
See also string-bytes, in Text Representations.
This function returns the element of sequence indexed by index. Legitimate values of index are integers ranging from 0 up to one less than the length of sequence. If sequence is a list, out-of-range values behave as for
nth. See Definition of nth. Otherwise, out-of-range values trigger anargs-out-of-rangeerror.(elt [1 2 3 4] 2) ⇒ 3 (elt '(1 2 3 4) 2) ⇒ 3 ;; We usestringto show clearly which charactereltreturns. (string (elt "1234" 2)) ⇒ "3" (elt [1 2 3 4] 4) error--> Args out of range: [1 2 3 4], 4 (elt [1 2 3 4] -1) error--> Args out of range: [1 2 3 4], -1This function generalizes
aref(see Array Functions) andnth(see Definition of nth).
Returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order.
Storing a new element into the copy does not affect the original sequence, and vice versa. However, the elements of the new sequence are not copies; they are identical (
eq) to the elements of the original. Therefore, changes made within these elements, as found via the copied sequence, are also visible in the original sequence.If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original's property list. However, the actual values of the properties are shared. See Text Properties.
This function does not work for dotted lists. Trying to copy a circular list may cause an infinite loop.
See also
appendin Building Lists,concatin Creating Strings, andvconcatin Vector Functions, for other ways to copy sequences.(setq bar '(1 2)) ⇒ (1 2) (setq x (vector 'foo bar)) ⇒ [foo (1 2)] (setq y (copy-sequence x)) ⇒ [foo (1 2)] (eq x y) ⇒ nil (equal x y) ⇒ t (eq (elt x 1) (elt y 1)) ⇒ t ;; Replacing an element of one sequence. (aset x 0 'quux) x ⇒ [quux (1 2)] y ⇒ [foo (1 2)] ;; Modifying the inside of a shared element. (setcar (aref x 1) 69) x ⇒ [quux (69 2)] y ⇒ [foo (69 2)]
An array object has slots that hold a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, the time to access an element of a list is proportional to the position of that element in the list.
Emacs defines four types of array, all one-dimensional:
strings (see 字符串类型), vectors (see 容器类型), bool-vectors (see 布尔容器类型), and
char-tables (see 字符表类型). Vectors and char-tables
can hold elements of any type, but strings can only hold characters,
and bool-vectors can only hold t and nil.
All four kinds of array share these characteristics:
aref and aset, respectively (see Array Functions).
When you create an array, other than a char-table, you must specify its length. You cannot specify the length of a char-table, because that is determined by the range of character codes.
In principle, if you want an array of text characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons:
By contrast, for an array of keyboard input characters (such as a key sequence), a vector may be necessary, because many keyboard input characters are outside the range that will fit in a string. See Key Sequence Input.
In this section, we describe the functions that accept all types of arrays.
This function returns
tif object is an array (i.e., a vector, a string, a bool-vector or a char-table).(arrayp [a]) ⇒ t (arrayp "asdf") ⇒ t (arrayp (syntax-table)) ;; A char-table. ⇒ t
This function returns the indexth element of array. The first element is at index zero.
(setq primes [2 3 5 7 11 13]) ⇒ [2 3 5 7 11 13] (aref primes 4) ⇒ 11 (aref "abcdefg" 1) ⇒ 98 ; ‘b’ is ASCII code 98.See also the function
elt, in Sequence Functions.
This function sets the indexth element of array to be object. It returns object.
(setq w [foo bar baz]) ⇒ [foo bar baz] (aset w 0 'fu) ⇒ fu w ⇒ [fu bar baz] (setq x "asdfasfd") ⇒ "asdfasfd" (aset x 3 ?Z) ⇒ 90 x ⇒ "asdZasfd"If array is a string and object is not a character, a
wrong-type-argumenterror results. The function converts a unibyte string to multibyte if necessary to insert a character.
This function fills the array array with object, so that each element of array is object. It returns array.
(setq a [a b c d e f g]) ⇒ [a b c d e f g] (fillarray a 0) ⇒ [0 0 0 0 0 0 0] a ⇒ [0 0 0 0 0 0 0] (setq s "When in the course") ⇒ "When in the course" (fillarray s ?-) ⇒ "------------------"If array is a string and object is not a character, a
wrong-type-argumenterror results.
The general sequence functions copy-sequence and length
are often useful for objects known to be arrays. See Sequence Functions.
A vector is a general-purpose array whose elements can be any Lisp objects. (By contrast, the elements of a string can only be characters. See Strings and Characters.) Vectors are used in Emacs for many purposes: as key sequences (see Key Sequences), as symbol-lookup tables (see Creating Symbols), as part of the representation of a byte-compiled function (see Byte Compilation), and more.
In Emacs Lisp, the indices of the elements of a vector start from zero and count up from there.
Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols a, b and
a is printed as [a b a]. You can write vectors in the
same way in Lisp input.
A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. This does not evaluate or even examine the elements of the vector. See Self-Evaluating Forms.
Here are examples illustrating these principles:
(setq avector [1 two '(three) "four" [five]])
⇒ [1 two (quote (three)) "four" [five]]
(eval avector)
⇒ [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
⇒ t
Here are some functions that relate to vectors:
This function returns
tif object is a vector.(vectorp [a]) ⇒ t (vectorp "asdf") ⇒ nil
This function creates and returns a vector whose elements are the arguments, objects.
(vector 'foo 23 [bar baz] "rats") ⇒ [foo 23 [bar baz] "rats"] (vector) ⇒ []
This function returns a new vector consisting of length elements, each initialized to object.
(setq sleepy (make-vector 9 'Z)) ⇒ [Z Z Z Z Z Z Z Z Z]
This function returns a new vector containing all the elements of sequences. The arguments sequences may be true lists, vectors, strings or bool-vectors. If no sequences are given, an empty vector is returned.
The value is a newly constructed vector that is not
eqto any existing vector.(setq a (vconcat '(A B C) '(D E F))) ⇒ [A B C D E F] (eq a (vconcat a)) ⇒ nil (vconcat) ⇒ [] (vconcat [A B C] "aa" '(foo (6 7))) ⇒ [A B C 97 97 foo (6 7)]The
vconcatfunction also allows byte-code function objects as arguments. This is a special feature to make it easy to access the entire contents of a byte-code function object. See Byte-Code Objects.For other concatenation functions, see
mapconcatin Mapping Functions,concatin Creating Strings, andappendin Building Lists.
The append function also provides a way to convert a vector into a
list with the same elements:
(setq avector [1 two (quote (three)) "four" [five]])
⇒ [1 two (quote (three)) "four" [five]]
(append avector nil)
⇒ (1 two (quote (three)) "four" [five])
A char-table is much like a vector, except that it is indexed by
character codes. Any valid character code, without modifiers, can be
used as an index in a char-table. You can access a char-table's
elements with aref and aset, as with any array. In
addition, a char-table can have extra slots to hold additional
data not associated with particular character codes. Like vectors,
char-tables are constants when evaluated, and can hold elements of any
type.
Each char-table has a subtype, a symbol, which serves two purposes:
display-table
as the subtype, and syntax tables are char-tables with
syntax-table as the subtype. The subtype can be queried using
the function char-table-subtype, described below.
char-table-extra-slots symbol property, which should be an
integer between 0 and 10. If the subtype has no such symbol property,
the char-table has no extra slots. See Property Lists, for
information about symbol properties.
A char-table can have a parent, which is another char-table. If
it does, then whenever the char-table specifies nil for a
particular character c, it inherits the value specified in the
parent. In other words, (aref char-table c) returns
the value from the parent of char-table if char-table itself
specifies nil.
A char-table can also have a default value. If so, then
(aref char-table c) returns the default value
whenever the char-table does not specify any other non-nil value.
Return a newly-created char-table, with subtype subtype (a symbol). Each element is initialized to init, which defaults to
nil. You cannot alter the subtype of a char-table after the char-table is created.There is no argument to specify the length of the char-table, because all char-tables have room for any valid character code as an index.
If subtype has the
char-table-extra-slotssymbol property, that specifies the number of extra slots in the char-table. This should be an integer between 0 and 10; otherwise,make-char-tableraises an error. If subtype has nochar-table-extra-slotssymbol property (see Property Lists), the char-table has no extra slots.
This function returns
tif object is a char-table, andnilotherwise.
There is no special function to access default values in a char-table.
To do that, use char-table-range (see below).
This function returns the parent of char-table. The parent is always either
nilor another char-table.
This function sets the parent of char-table to new-parent.
This function returns the contents of extra slot n of char-table. The number of extra slots in a char-table is determined by its subtype.
This function stores value in extra slot n of char-table.
A char-table can specify an element value for a single character code; it can also specify a value for an entire character set.
This returns the value specified in char-table for a range of characters range. Here are the possibilities for range:
nil- Refers to the default value.
- char
- Refers to the element for character char (supposing char is a valid character code).
(from.to)- A cons cell refers to all the characters in the inclusive range ‘[from..to]’.
This function sets the value in char-table for a range of characters range. Here are the possibilities for range:
nil- Refers to the default value.
t- Refers to the whole range of character codes.
- char
- Refers to the element for character char (supposing char is a valid character code).
(from.to)- A cons cell refers to all the characters in the inclusive range ‘[from..to]’.
This function calls its argument function for each element of char-table that has a non-
nilvalue. The call to function is with two arguments, a key and a value. The key is a possible range argument forchar-table-range—either a valid character or a cons cell(from.to), specifying a range of characters that share the same value. The value is what(char-table-rangechar-table key)returns.Overall, the key-value pairs passed to function describe all the values stored in char-table.
The return value is always
nil; to make calls tomap-char-tableuseful, function should have side effects. For example, here is how to examine the elements of the syntax table:(let (accumulator) (map-char-table #'(lambda (key value) (setq accumulator (cons (list (if (consp key) (list (car key) (cdr key)) key) value) accumulator))) (syntax-table)) accumulator) ⇒ (((2597602 4194303) (2)) ((2597523 2597601) (3)) ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1)) ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
A bool-vector is much like a vector, except that it stores only the
values t and nil. If you try to store any non-nil
value into an element of the bool-vector, the effect is to store
t there. As with all arrays, bool-vector indices start from 0,
and the length cannot be changed once the bool-vector is created.
Bool-vectors are constants when evaluated.
There are two special functions for working with bool-vectors; aside from that, you manipulate them with same functions used for other kinds of arrays.
Return a new bool-vector of length elements, each one initialized to initial.
Here is an example of creating, examining, and updating a bool-vector. Note that the printed form represents up to 8 boolean values as a single character.
(setq bv (make-bool-vector 5 t))
⇒ #&5"^_"
(aref bv 1)
⇒ t
(aset bv 3 nil)
⇒ nil
bv
⇒ #&5"^W"
These results make sense because the binary codes for control-_ and control-W are 11111 and 10111, respectively.
A hash table is a very fast kind of lookup table, somewhat like an alist (see Association Lists) in that it maps keys to corresponding values. It differs from an alist in these ways:
Emacs Lisp provides a general-purpose hash table data type, along with a series of functions for operating on them. Hash tables have a special printed representation, which consists of ‘#s’ followed by a list specifying the hash table properties and contents. See Creating Hash. (Note that the term “hash notation”, which refers to the initial ‘#’ character used in the printed representations of objects with no read representation, has nothing to do with the term “hash table”. See 打印表示.)
Obarrays are also a kind of hash table, but they are a different type of object and are used only for recording interned symbols (see Creating Symbols).
The principal function for creating a hash table is
make-hash-table.
This function creates a new hash table according to the specified arguments. The arguments should consist of alternating keywords (particular symbols recognized specially) and values corresponding to them.
Several keywords make sense in
make-hash-table, but the only two that you really need to know about are:testand:weakness.
:testtest- This specifies the method of key lookup for this hash table. The default is
eql;eqandequalare other alternatives:
eql- Keys which are numbers are “the same” if they are
equal, that is, if they are equal in value and either both are integers or both are floating point numbers; otherwise, two distinct objects are never “the same.”eq- Any two distinct Lisp objects are “different” as keys.
equal- Two Lisp objects are “the same,” as keys, if they are equal according to
equal.You can use
define-hash-table-test(see Defining Hash) to define additional possibilities for test.:weaknessweak- The weakness of a hash table specifies whether the presence of a key or value in the hash table preserves it from garbage collection.
The value, weak, must be one of
nil,key,value,key-or-value,key-and-value, ortwhich is an alias forkey-and-value. If weak iskeythen the hash table does not prevent its keys from being collected as garbage (if they are not referenced anywhere else); if a particular key does get collected, the corresponding association is removed from the hash table.If weak is
value, then the hash table does not prevent values from being collected as garbage (if they are not referenced anywhere else); if a particular value does get collected, the corresponding association is removed from the hash table.If weak is
key-and-valueort, both the key and the value must be live in order to preserve the association. Thus, the hash table does not protect either keys or values from garbage collection; if either one is collected as garbage, that removes the association.If weak is
key-or-value, either the key or the value can preserve the association. Thus, associations are removed from the hash table when both their key and value would be collected as garbage (if not for references from weak hash tables).The default for weak is
nil, so that all keys and values referenced in the hash table are preserved from garbage collection.:sizesize- This specifies a hint for how many associations you plan to store in the hash table. If you know the approximate number, you can make things a little more efficient by specifying it this way. If you specify too small a size, the hash table will grow automatically when necessary, but doing that takes some extra time.
The default size is 65.
:rehash-sizerehash-size- When you add an association to a hash table and the table is “full,” it grows automatically. This value specifies how to make the hash table larger, at that time.
If rehash-size is an integer, it should be positive, and the hash table grows by adding that much to the nominal size. If rehash-size is a floating point number, it had better be greater than 1, and the hash table grows by multiplying the old size by that number.
The default value is 1.5.
:rehash-thresholdthreshold- This specifies the criterion for when the hash table is “full” (so it should be made larger). The value, threshold, should be a positive floating point number, no greater than 1. The hash table is “full” whenever the actual number of entries exceeds this fraction of the nominal size. The default for threshold is 0.8.
This is equivalent to
make-hash-table, but with a different style argument list. The argument test specifies the method of key lookup.This function is obsolete. Use
make-hash-tableinstead.
You can also create a new hash table using the printed representation
for hash tables. The Lisp reader can read this printed
representation, provided each element in the specified hash table has
a valid read syntax (see 打印表示). For instance,
the following specifies a new hash table containing the keys
key1 and key2 (both symbols) associated with val1
(a symbol) and 300 (a number) respectively.
#s(hash-table size 30 data (key1 val1 key2 300))
The printed representation for a hash table consists of ‘#s’
followed by a list beginning with ‘hash-table’. The rest of the
list should consist of zero or more property-value pairs specifying
the hash table's properties and initial contents. The properties and
values are read literally. Valid property names are size,
test, weakness, rehash-size,
rehash-threshold, and data. The data property
should be a list of key-value pairs for the initial contents; the
other properties have the same meanings as the matching
make-hash-table keywords (:size, :test, etc.),
described above.
Note that you cannot specify a hash table whose initial contents include objects that have no read syntax, such as buffers and frames. Such objects may be added to the hash table after it is created.
This section describes the functions for accessing and storing associations in a hash table. In general, any Lisp object can be used as a hash key, unless the comparison method imposes limits. Any Lisp object can also be used as the value.
This function looks up key in table, and returns its associated value—or default, if key has no association in table.
This function enters an association for key in table, with value value. If key already has an association in table, value replaces the old associated value.
This function removes the association for key from table, if there is one. If key has no association,
remhashdoes nothing.Common Lisp note: In Common Lisp,
remhashreturns non-nilif it actually removed an association andnilotherwise. In Emacs Lisp,remhashalways returnsnil.
This function removes all the associations from hash table table, so that it becomes empty. This is also called clearing the hash table.
Common Lisp note: In Common Lisp,
clrhashreturns the empty table. In Emacs Lisp, it returnsnil.
This function calls function once for each of the associations in table. The function function should accept two arguments—a key listed in table, and its associated value.
maphashreturnsnil.
You can define new methods of key lookup by means of
define-hash-table-test. In order to use this feature, you need
to understand how hash tables work, and what a hash code means.
You can think of a hash table conceptually as a large array of many
slots, each capable of holding one association. To look up a key,
gethash first computes an integer, the hash code, from the key.
It reduces this integer modulo the length of the array, to produce an
index in the array. Then it looks in that slot, and if necessary in
other nearby slots, to see if it has found the key being sought.
Thus, to define a new method of key lookup, you need to specify both a function to compute the hash code from a key, and a function to compare two keys directly.
This function defines a new hash table test, named name.
After defining name in this way, you can use it as the test argument in
make-hash-table. When you do that, the hash table will use test-fn to compare key values, and hash-fn to compute a “hash code” from a key value.The function test-fn should accept two arguments, two keys, and return non-
nilif they are considered “the same.”The function hash-fn should accept one argument, a key, and return an integer that is the “hash code” of that key. For good results, the function should use the whole range of integer values for hash codes, including negative integers.
The specified functions are stored in the property list of name under the property
hash-table-test; the property value's form is(test-fn hash-fn).
This function returns a hash code for Lisp object obj. This is an integer which reflects the contents of obj and the other Lisp objects it points to.
If two objects obj1 and obj2 are equal, then
(sxhashobj1)and(sxhashobj2)are the same integer.If the two objects are not equal, the values returned by
sxhashare usually different, but not always; once in a rare while, by luck, you will encounter two distinct-looking objects that give the same result fromsxhash.
This example creates a hash table whose keys are strings that are compared case-insensitively.
(defun case-fold-string= (a b)
(compare-strings a nil nil b nil nil t))
(defun case-fold-string-hash (a)
(sxhash (upcase a)))
(define-hash-table-test 'case-fold
'case-fold-string= 'case-fold-string-hash)
(make-hash-table :test 'case-fold)
Here is how you could define a hash table test equivalent to the
predefined test value equal. The keys can be any Lisp object,
and equal-looking objects are considered the same key.
(define-hash-table-test 'contents-hash 'equal 'sxhash)
(make-hash-table :test 'contents-hash)
Here are some other functions for working with hash tables.
This function creates and returns a copy of table. Only the table itself is copied—the keys and values are shared.
This returns the test value that was given when table was created, to specify how to hash and compare keys. See
make-hash-table(see Creating Hash).
This function returns the weak value that was specified for hash table table.
A symbol is an object with a unique name. This chapter describes symbols, their components, their property lists, and how they are created and interned. Separate chapters describe the use of symbols as variables and as function names; see Variables, and Functions. For the precise read syntax for symbols, see 符号类型.
You can test whether an arbitrary Lisp object is a symbol
with symbolp:
Each symbol has four components (or “cells”), each of which references another object:
symbol-name in Creating Symbols.
symbol-value in
Accessing Variables.
symbol-function in Function Cells.
symbol-plist in Property Lists.
The print name cell always holds a string, and cannot be changed. The other three cells can be set individually to any specified Lisp object.
The print name cell holds the string that is the name of the symbol. Since symbols are represented textually by their names, it is important not to have two symbols with the same name. The Lisp reader ensures this: every time it reads a symbol, it looks for an existing symbol with the specified name before it creates a new one. (In GNU Emacs Lisp, this lookup uses a hashing algorithm and an obarray; see Creating Symbols.)
The value cell holds the symbol's value as a variable
(see Variables). That is what you get if you evaluate the symbol as
a Lisp expression (see Evaluation). Any Lisp object is a legitimate
value. Certain symbols have values that cannot be changed; these
include nil and t, and any symbol whose name starts with
‘:’ (those are called keywords). See Constant Variables.
We often refer to “the function foo” when we really mean
the function stored in the function cell of the symbol foo. We
make the distinction explicit only when necessary. In normal
usage, the function cell usually contains a function
(see Functions) or a macro (see Macros), as that is what the
Lisp interpreter expects to see there (see Evaluation). Keyboard
macros (see Keyboard Macros), keymaps (see Keymaps) and
autoload objects (see Autoloading) are also sometimes stored in
the function cells of symbols.
The property list cell normally should hold a correctly formatted property list (see Property Lists), as a number of functions expect to see a property list there.
The function cell or the value cell may be void, which means
that the cell does not reference any object. (This is not the same
thing as holding the symbol void, nor the same as holding the
symbol nil.) Examining a function or value cell that is void
results in an error, such as ‘Symbol's value as variable is void’.
The four functions symbol-name, symbol-value,
symbol-plist, and symbol-function return the contents of
the four cells of a symbol. Here as an example we show the contents of
the four cells of the symbol buffer-file-name:
(symbol-name 'buffer-file-name)
⇒ "buffer-file-name"
(symbol-value 'buffer-file-name)
⇒ "/gnu/elisp/symbols.texi"
(symbol-function 'buffer-file-name)
⇒ #<subr buffer-file-name>
(symbol-plist 'buffer-file-name)
⇒ (variable-documentation 29529)
Because this symbol is the variable which holds the name of the file
being visited in the current buffer, the value cell contents we see are
the name of the source file of this chapter of the Emacs Lisp Manual.
The property list cell contains the list (variable-documentation
29529) which tells the documentation functions where to find the
documentation string for the variable buffer-file-name in the
DOC-version file. (29529 is the offset from the beginning
of the DOC-version file to where that documentation string
begins—see Documentation Basics.) The function cell contains
the function for returning the name of the file.
buffer-file-name names a primitive function, which has no read
syntax and prints in hash notation (see 原始函数类型). A
symbol naming a function written in Lisp would have a lambda expression
(or a byte-code object) in this cell.
A definition in Lisp is a special form that announces your intention to use a certain symbol in a particular way. In Emacs Lisp, you can define a symbol as a variable, or define it as a function (or macro), or both independently.
A definition construct typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable.
defvar and defconst are special forms that define a
symbol as a global variable. They are documented in detail in
Defining Variables. For defining user option variables that can
be customized, use defcustom (see Customization).
defun defines a symbol as a function, creating a lambda
expression and storing it in the function cell of the symbol. This
lambda expression thus becomes the function definition of the symbol.
(The term “function definition,” meaning the contents of the function
cell, is derived from the idea that defun gives the symbol its
definition as a function.) defsubst and defalias are two
other ways of defining a function. See Functions.
defmacro defines a symbol as a macro. It creates a macro
object and stores it in the function cell of the symbol. Note that a
given symbol can be a macro or a function, but not both at once, because
both macro and function definitions are kept in the function cell, and
that cell can hold only one Lisp object at any given time.
See Macros.
In Emacs Lisp, a definition is not required in order to use a symbol
as a variable or function. Thus, you can make a symbol a global
variable with setq, whether you define it first or not. The real
purpose of definitions is to guide programmers and programming tools.
They inform programmers who read the code that certain symbols are
intended to be used as variables, or as functions. In addition,
utilities such as etags and make-docfile recognize
definitions, and add appropriate information to tag tables and the
DOC-version file. See Accessing Documentation.
To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion.
When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it “hashes” those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J's and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name's hash code. (The same idea is used for general Emacs hash tables, but they are a different data type; see Hash Tables.)
If a symbol with the desired name is found, the reader uses that symbol. If the obarray does not contain a symbol with that name, the reader makes a new symbol and adds it to the obarray. Finding or adding a symbol with a certain name is called interning it, and the symbol is then called an interned symbol.
Interning ensures that each obarray has just one symbol with any particular name. Other like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same symbols for the same names, as long as you keep reading with the same obarray.
Interning usually happens automatically in the reader, but sometimes other programs need to do it. For example, after the M-x command obtains the command name as a string using the minibuffer, it then interns the string, to get the interned symbol with that name.
No obarray contains all symbols; in fact, some symbols are not in any obarray. They are called uninterned symbols. An uninterned symbol has the same four cells as other symbols; however, the only way to gain access to it is by finding it in some other object or as the value of a variable.
Creating an uninterned symbol is useful in generating Lisp code, because an uninterned symbol used as a variable in the code you generate cannot clash with any variables used in other Lisp programs.
In Emacs Lisp, an obarray is actually a vector. Each element of the
vector is a bucket; its value is either an interned symbol whose name
hashes to that bucket, or 0 if the bucket is empty. Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket. Because these links are invisible, there is no way to
find all the symbols in an obarray except using mapatoms (below).
The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, so you can create an obarray
with (make-vector length 0). This is the only
valid way to create an obarray. Prime numbers as lengths tend
to result in good hashing; lengths one less than a power of two are also
good.
Do not try to put symbols in an obarray yourself. This does
not work—only intern can enter a symbol in an obarray properly.
Common Lisp note: In Common Lisp, a single symbol may be interned in several obarrays.
Most of the functions below take a name and sometimes an obarray as
arguments. A wrong-type-argument error is signaled if the name
is not a string, or if the obarray is not a vector.
This function returns the string that is symbol's name. For example:
(symbol-name 'foo) ⇒ "foo"Warning: Changing the string by substituting characters does change the name of the symbol, but fails to update the obarray, so don't do it!
This function returns a newly-allocated, uninterned symbol whose name is name (which must be a string). Its value and function definition are void, and its property list is
nil. In the example below, the value ofsymis noteqtofoobecause it is a distinct uninterned symbol whose name is also ‘foo’.(setq sym (make-symbol "foo")) ⇒ foo (eq sym 'foo) ⇒ nil
This function returns the interned symbol whose name is name. If there is no such symbol in the obarray obarray,
interncreates a new one, adds it to the obarray, and returns it. If obarray is omitted, the value of the global variableobarrayis used.(setq sym (intern "foo")) ⇒ foo (eq sym 'foo) ⇒ t (setq sym1 (intern "foo" other-obarray)) ⇒ foo (eq sym1 'foo) ⇒ nil
Common Lisp note: In Common Lisp, you can intern an existing symbol
in an obarray. In Emacs Lisp, you cannot do this, because the argument
to intern must be a string, not a symbol.
This function returns the symbol in obarray whose name is name, or
nilif obarray has no symbol with that name. Therefore, you can useintern-softto test whether a symbol with a given name is already interned. If obarray is omitted, the value of the global variableobarrayis used.The argument name may also be a symbol; in that case, the function returns name if name is interned in the specified obarray, and otherwise
nil.(intern-soft "frazzle") ; No such symbol exists. ⇒ nil (make-symbol "frazzle") ; Create an uninterned one. ⇒ frazzle (intern-soft "frazzle") ; That one cannot be found. ⇒ nil (setq sym (intern "frazzle")) ; Create an interned one. ⇒ frazzle (intern-soft "frazzle") ; That one can be found! ⇒ frazzle (eq sym 'frazzle) ; And it is the same one. ⇒ t
This function calls function once with each symbol in the obarray obarray. Then it returns
nil. If obarray is omitted, it defaults to the value ofobarray, the standard obarray for ordinary symbols.(setq count 0) ⇒ 0 (defun count-syms (s) (setq count (1+ count))) ⇒ count-syms (mapatoms 'count-syms) ⇒ nil count ⇒ 1871See
documentationin Accessing Documentation, for another example usingmapatoms.
This function deletes symbol from the obarray obarray. If
symbolis not actually in the obarray,uninterndoes nothing. If obarray isnil, the current obarray is used.If you provide a string instead of a symbol as symbol, it stands for a symbol name. Then
uninterndeletes the symbol (if any) in the obarray which has that name. If there is no such symbol,uninterndoes nothing.If
uninterndoes delete a symbol, it returnst. Otherwise it returnsnil.
A property list (plist for short) is a list of paired elements. Each of the pairs associates a property name (usually a symbol) with a property or value.
Every symbol has a cell that stores a property list (see Symbol Components). This property list is used to record information about the symbol, such as its variable documentation and the name of the file where it was defined.
Property lists can also be used in other contexts. For instance, you can assign property lists to character positions in a string or buffer. See Text Properties.
The property names and values in a property list can be any Lisp
objects, but the names are usually symbols. Property list functions
compare the property names using eq. Here is an example of a
property list, found on the symbol progn when the compiler is
loaded:
(lisp-indent-function 0 byte-compile byte-compile-progn)
Here lisp-indent-function and byte-compile are property
names, and the other two elements are the corresponding values.
Association lists (see Association Lists) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant since the property names must be distinct.
Property lists are better than association lists for attaching
information to various Lisp function names or variables. If your
program keeps all of its associations in one association list, it will
typically need to search that entire list each time it checks for an
association. This could be slow. By contrast, if you keep the same
information in the property lists of the function names or variables
themselves, each search will scan only the length of one property list,
which is usually short. This is why the documentation for a variable is
recorded in a property named variable-documentation. The byte
compiler likewise uses properties to record those functions needing
special treatment.
However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to choose property names that are probably unique, such as by beginning the property name with the program's usual name-prefix for variables and functions.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list.
This function sets symbol's property list to plist. Normally, plist should be a well-formed property list, but this is not enforced. The return value is plist.
(setplist 'foo '(a 1 b (2 3) c nil)) ⇒ (a 1 b (2 3) c nil) (symbol-plist 'foo) ⇒ (a 1 b (2 3) c nil)For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see Abbrevs).
This function finds the value of the property named property in symbol's property list. If there is no such property,
nilis returned. Thus, there is no distinction between a value ofniland the absence of the property.The name property is compared with the existing property names using
eq, so any object is a legitimate property.See
putfor an example.
This function puts value onto symbol's property list under the property name property, replacing any previous property value. The
putfunction returns value.(put 'fly 'verb 'transitive) ⇒'transitive (put 'fly 'noun '(a buzzing little bug)) ⇒ (a buzzing little bug) (get 'fly 'verb) ⇒ transitive (symbol-plist 'fly) ⇒ (verb transitive noun (a buzzing little bug))
These functions are useful for manipulating property lists that are stored in places other than symbols:
This returns the value of the property property stored in the property list plist. It accepts a malformed plist argument. If property is not found in the plist, it returns
nil. For example,(plist-get '(foo 4) 'foo) ⇒ 4 (plist-get '(foo 4 bad) 'foo) ⇒ 4 (plist-get '(foo 4 bad) 'bad) ⇒nil(plist-get '(foo 4 bad) 'bar) ⇒ nil
This stores value as the value of the property property in the property list plist. It may modify plist destructively, or it may construct a new list structure without altering the old. The function returns the modified property list, so you can store that back in the place where you got plist. For example,
(setq my-plist '(bar t foo 4)) ⇒ (bar t foo 4) (setq my-plist (plist-put my-plist 'foo 69)) ⇒ (bar t foo 69) (setq my-plist (plist-put my-plist 'quux '(a))) ⇒ (bar t foo 69 quux (a))
You could define put in terms of plist-put as follows:
(defun put (symbol prop value)
(setplist symbol
(plist-put (symbol-plist symbol) prop value)))
Like
plist-getexcept that it compares properties usingequalinstead ofeq.
Like
plist-putexcept that it compares properties usingequalinstead ofeq.
This returns non-
nilif plist contains the given property. Unlikeplist-get, this allows you to distinguish between a missing property and a property with the valuenil. The value is actually the tail of plist whosecaris property.
The evaluation of expressions in Emacs Lisp is performed by the
Lisp interpreter—a program that receives a Lisp object as input
and computes its value as an expression. How it does this depends
on the data type of the object, according to rules described in this
chapter. The interpreter runs automatically to evaluate portions of
your program, but can also be called explicitly via the Lisp primitive
function eval.
The Lisp interpreter, or evaluator, is the part of Emacs that computes the value of an expression that is given to it. When a function written in Lisp is called, the evaluator computes the value of the function by evaluating the expressions in the function body. Thus, running any Lisp program really means running the Lisp interpreter.
A Lisp object that is intended for evaluation is called an expression or a form. The fact that forms are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often.
In subsequent sections, we will describe the details of what evaluation means for each kind of form.
It is very common to read a Lisp form and then evaluate the form,
but reading and evaluation are separate activities, and either can be
performed alone. Reading per se does not evaluate anything; it
converts the printed representation of a Lisp object to the object
itself. It is up to the caller of read to specify whether this
object is a form to be evaluated, or serves some entirely different
purpose. See Input Functions.
Evaluation is a recursive process, and evaluating a form often
involves evaluating parts within that form. For instance, when you
evaluate a function call form such as (car x), Emacs
first evaluates the argument (the subform x). After evaluating
the argument, Emacs executes the function (car), and if
the function is written in Lisp, execution works by evaluating the
body of the function. (In this example, however, car is
not a Lisp function; it is a primitive function implemented in C.)
See Functions, for more information about functions and function
calls.
Evaluation takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables (see Variables).3 Whenever a form refers to a variable without creating a new binding for it, the variable evaluates to the value given by the current environment. Evaluating a form may create a new environment for recursive evaluation, by binding variables (see Local Variables). Such environments are temporary, and vanish when the evaluation of the form is complete.
Evaluating a form may also make changes that persist; these changes
are called side effects. An example of a form that produces a
side effect is (setq foo 1).
Do not confuse evaluation with command key interpretation. The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses call-interactively to execute that command. Executing the
command usually involves evaluation, if the command is written in
Lisp; however, this step is not considered a part of command key
interpretation. See Command Loop.
A Lisp object that is intended to be evaluated is called a form. How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and “all other types.” This section describes all three kinds, one by one, starting with the “all other types” which are self-evaluating forms.
A self-evaluating form is any form that is not a list or
symbol. Self-evaluating forms evaluate to themselves: the result of
evaluation is the same object that was evaluated. Thus, the number 25
evaluates to 25, and the string "foo" evaluates to the string
"foo". Likewise, evaluating a vector does not cause evaluation
of the elements of the vector—it returns the same vector with its
contents unchanged.
'123 ; A number, shown without evaluation. ⇒ 123 123 ; Evaluated as usual---result is the same. ⇒ 123 (eval '123) ; Evaluated ``by hand''---result is the same. ⇒ 123 (eval (eval '123)) ; Evaluating twice changes nothing. ⇒ 123
It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because there's no way to write them textually. It is possible to construct Lisp expressions containing these types by means of a Lisp program. Here is an example:
;; Build an expression containing a buffer object. (setq print-exp (list 'print (current-buffer))) ⇒ (print #<buffer eval.texi>) ;; Evaluate it. (eval print-exp) -| #<buffer eval.texi> ⇒ #<buffer eval.texi>
When a symbol is evaluated, it is treated as a variable. The result is the variable's value, if it has one. If it has none (if its value cell is void), an error is signaled. For more information on the use of variables, see Variables.
In the following example, we set the value of a symbol with
setq. Then we evaluate the symbol, and get back the value that
setq stored.
(setq a 123)
⇒ 123
(eval 'a)
⇒ 123
a
⇒ 123
The symbols nil and t are treated specially, so that the
value of nil is always nil, and the value of t is
always t; you cannot set or bind them to any other values. Thus,
these two symbols act like self-evaluating forms, even though
eval treats them like any other symbol. A symbol whose name
starts with ‘:’ also self-evaluates in the same way; likewise,
its value ordinarily cannot be changed. See Constant Variables.
A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The remaining list elements constitute the arguments for the function, macro, or special form.
The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects such as Scheme.
If the first element of the list is a symbol then evaluation examines the symbol's function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until it obtains a non-symbol. See Function Names, for more information about symbol function indirection.
One possible consequence of this process is an infinite loop, in the
event that a symbol's function cell refers to the same symbol. Or a
symbol may have a void function cell, in which case the subroutine
symbol-function signals a void-function error. But if
neither of these things happens, we eventually obtain a non-symbol,
which ought to be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro,
a special form, or an autoload object. Each of these types is a case
described in one of the following sections. If the object is not one
of these types, Emacs signals an invalid-function error.
The following example illustrates the symbol indirection process. We
use fset to set the function cell of a symbol and
symbol-function to get the function cell contents
(see Function Cells). Specifically, we store the symbol car
into the function cell of first, and the symbol first into
the function cell of erste.
;; Build this function cell linkage:
;; ------------- ----- ------- -------
;; | #<subr car> | <-- | car | <-- | first | <-- | erste |
;; ------------- ----- ------- -------
(symbol-function 'car)
⇒ #<subr car>
(fset 'first 'car)
⇒ car
(fset 'erste 'first)
⇒ first
(erste '(1 2 3)) ; Call the function referenced by erste.
⇒ 1
By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol.
((lambda (arg) (erste arg))
'(1 2 3))
⇒ 1
Executing the function itself evaluates its body; this does involve
symbol function indirection when calling erste.
The built-in function indirect-function provides an easy way to
perform symbol function indirection explicitly.
This function returns the meaning of function as a function. If function is a symbol, then it finds function's function definition and starts over with that value. If function is not a symbol, then it returns function itself.
This function signals a
void-functionerror if the final symbol is unbound and optional argument noerror isnilor omitted. Otherwise, if noerror is non-nil, it returnsnilif the final symbol is unbound.It signals a
cyclic-function-indirectionerror if there is a loop in the chain of symbols.Here is how you could define
indirect-functionin Lisp:(defun indirect-function (function) (if (symbolp function) (indirect-function (symbol-function function)) function))
If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a function call. For example, here is a call to the function
+:
(+ 1 x)
The first step in evaluating a function call is to evaluate the
remaining elements of the list from left to right. The results are the
actual argument values, one value for each list element. The next step
is to call the function with this list of arguments, effectively using
the function apply (see Calling Functions). If the function
is written in Lisp, the arguments are used to bind the argument
variables of the function (see Lambda Expressions); then the forms
in the function body are evaluated in order, and the value of the last
body form becomes the value of the function call.
If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, to be evaluated in place of the original form. The expansion may be any sort of form: a self-evaluating constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results.
Ordinary evaluation of a macro call finishes by evaluating the expansion. However, the macro expansion is not necessarily evaluated right away, or at all, because other programs also expand macro calls, and they may or may not evaluate the expansions.
Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are computed when the expansion is evaluated.
For example, given a macro defined as follows:
(defmacro cadr (x)
(list 'car (list 'cdr x)))
an expression such as (cadr (assq 'handler list)) is a macro
call, and its expansion is:
(car (cdr (assq 'handler list)))
Note that the argument (assq 'handler list) appears in the
expansion.
See Macros, for a complete description of Emacs Lisp macros.
A special form is a primitive function specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings—things which functions cannot do.
Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.
Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described.
andcatchcondcondition-casedefconstdefmacrodefundefvarfunctionifinteractiveletlet*orprog1prog2prognquotesave-current-buffersave-excursionsave-restrictionsave-window-excursionsetqsetq-defaulttrack-mouseunwind-protectwhilewith-output-to-temp-bufferCommon Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp.setq,if, andcatchare special forms in both Emacs Lisp and Common Lisp.defunis a special form in Emacs Lisp, but a macro in Common Lisp.save-excursionis a special form in Emacs Lisp, but doesn't exist in Common Lisp.throwis a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn't have multiple values).
The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. It specifies which file contains the definition. When an autoload object appears as a symbol's function definition, calling that symbol as a function automatically loads the specified file; then it calls the real definition loaded from that file. See Autoload.
The special form quote returns its single argument, as written,
without evaluating it. This provides a way to include constant symbols
and lists, which are not self-evaluating objects, in a program. (It is
not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)
Because quote is used so often in programs, Lisp provides a
convenient read syntax for it. An apostrophe character (‘'’)
followed by a Lisp object (in read syntax) expands to a list whose first
element is quote, and whose second element is the object. Thus,
the read syntax 'x is an abbreviation for (quote x).
Here are some examples of expressions that use quote:
(quote (+ 1 2))
⇒ (+ 1 2)
(quote foo)
⇒ foo
'foo
⇒ foo
''foo
⇒ (quote foo)
'(quote foo)
⇒ (quote foo)
['foo]
⇒ [(quote foo)]
Other quoting constructs include function (see Anonymous Functions), which causes an anonymous lambda expression written in Lisp
to be compiled, and ‘`’ (see Backquote), which is used to quote
only part of a list, while computing and substituting other parts.
Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run. On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list. On these occasions, use the eval function.
The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see Loading).
It is generally cleaner and more flexible to store a function in a
data structure, and call it with funcall or apply, than
to store an expression in the data structure and evaluate it. Using
functions provides the ability to pass information to them as
arguments.
This is the basic function evaluating an expression. It evaluates form in the current environment and returns the result. How the evaluation proceeds depends on the type of the object (see Forms).
Since
evalis a function, the argument expression that appears in a call toevalis evaluated twice: once as preparation beforeevalis called, and again by theevalfunction itself. Here is an example:(setq foo 'bar) ⇒ bar (setq bar 'baz) ⇒ baz ;; Hereevalreceives argumentfoo(eval 'foo) ⇒ bar ;; Hereevalreceives argumentbar, which is the value offoo(eval foo) ⇒ bazThe number of currently active calls to
evalis limited tomax-lisp-eval-depth(see below).
This function evaluates the forms in the current buffer in the region defined by the positions start and end. It reads forms from the region and calls
evalon them until the end of the region is reached, or until an error is signaled and not handled.By default,
eval-regiondoes not produce any output. However, if stream is non-nil, any output produced by output functions (see Output Functions), as well as the values that result from evaluating the expressions in the region are printed using stream. See Output Streams.If read-function is non-
nil, it should be a function, which is used instead ofreadto read expressions one by one. This function is called with one argument, the stream for reading input. You can also use the variableload-read-function(see How Programs Do Loading) to specify this function, but it is more robust to use the read-function argument.
eval-regiondoes not move point. It always returnsnil.
This is similar to
eval-region, but the arguments provide different optional features.eval-bufferoperates on the entire accessible portion of buffer buffer-or-name. buffer-or-name can be a buffer, a buffer name (a string), ornil(or omitted), which means to use the current buffer. stream is used as ineval-region, unless stream isniland print non-nil. In that case, values that result from evaluating the expressions are still discarded, but the output of the output functions is printed in the echo area. filename is the file name to use forload-history(see Unloading), and defaults tobuffer-file-name(see Buffer File Name). If unibyte is non-nil,readconverts strings to unibyte whenever possible.
This variable defines the maximum depth allowed in calls to
eval,apply, andfuncallbefore an error is signaled (with error message"Lisp nesting exceeds max-lisp-eval-depth").This limit, with the associated error when it is exceeded, is one way Emacs Lisp avoids infinite recursion on an ill-defined function. If you increase the value of
max-lisp-eval-depthtoo much, such code can cause stack overflow instead. The depth limit counts internal uses ofeval,apply, andfuncall, such as for calling the functions mentioned in Lisp expressions, and recursive evaluation of function call arguments and function body forms, as well as explicit calls in Lisp code.The default value of this variable is 400. If you set it to a value less than 100, Lisp will reset it to 100 if the given value is reached. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
max-specpdl-sizeprovides another limit on nesting. See Local Variables.
The value of this variable is a list of the values returned by all the expressions that were read, evaluated, and printed from buffers (including the minibuffer) by the standard Emacs commands which do this. (Note that this does not include evaluation in ‘*ielm*’ buffers, nor evaluation using C-j in
lisp-interaction-mode.) The elements are ordered most recent first.(setq x 1) ⇒ 1 (list 'A (1+ 2) auto-save-default) ⇒ (A 3 t) values ⇒ ((A 3 t) 1 ...)This variable is useful for referring back to values of forms recently evaluated. It is generally a bad idea to print the value of
valuesitself, since this may be very long. Instead, examine particular elements, like this:;; Refer to the most recent evaluation result. (nth 0 values) ⇒ (A 3 t) ;; That put a new element on, ;; so all elements move back one. (nth 1 values) ⇒ (A 3 t) ;; This gets the element that was next-to-most-recent ;; before this example. (nth 3 values) ⇒ 1
A Lisp program consists of expressions or forms (see Forms). We control the order of execution of these forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain.
The simplest order of execution is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code—the forms are executed in the order written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b. The result of evaluating b becomes the value of the function.
Explicit control structures make possible an order of execution other than sequential.
Emacs Lisp provides several kinds of control structure, including other varieties of sequencing, conditionals, iteration, and (controlled) jumps—all discussed below. The built-in control structures are special forms since their subforms are not necessarily evaluated or not evaluated sequentially. You can use macros to define your own control structure constructs (see Macros).
Evaluating forms in the order they appear is the most common way
control passes from one form to another. In some contexts, such as in a
function body, this happens automatically. Elsewhere you must use a
control structure construct to do this: progn, the simplest
control construct of Lisp.
A progn special form looks like this:
(progn a b c ...)
and it says to execute the forms a, b, c, and so on, in
that order. These forms are called the body of the progn form.
The value of the last form in the body becomes the value of the entire
progn. (progn) returns nil.
In the early days of Lisp, progn was the only way to execute
two or more forms in succession and use the value of the last of them.
But programmers found they often needed to use a progn in the
body of a function, where (at that time) only one form was allowed. So
the body of a function was made into an “implicit progn”:
several forms are allowed just as in the body of an actual progn.
Many other control structures likewise contain an implicit progn.
As a result, progn is not used as much as it was many years ago.
It is needed now most often inside an unwind-protect, and,
or, or in the then-part of an if.
This special form evaluates all of the forms, in textual order, returning the result of the final form.
(progn (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" ⇒ "The third form"
Two other control constructs likewise evaluate a series of forms but return a different value:
This special form evaluates form1 and all of the forms, in textual order, returning the result of form1.
(prog1 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" ⇒ "The first form"Here is a way to remove the first element from a list in the variable
x, then return the value of that former element:(prog1 (car x) (setq x (cdr x)))
This special form evaluates form1, form2, and all of the following forms, in textual order, returning the result of form2.
(prog2 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" ⇒ "The second form"
Conditional control structures choose among alternatives. Emacs Lisp
has four conditional forms: if, which is much the same as in
other languages; when and unless, which are variants of
if; and cond, which is a generalized case statement.
ifchooses between the then-form and the else-forms based on the value of condition. If the evaluated condition is non-nil, then-form is evaluated and the result returned. Otherwise, the else-forms are evaluated in textual order, and the value of the last one is returned. (The else part ofifis an example of an implicitprogn. See Sequencing.)If condition has the value
nil, and no else-forms are given,ifreturnsnil.
ifis a special form because the branch that is not selected is never evaluated—it is ignored. Thus, in the example below,trueis not printed because(if nil (print 'true) 'very-false) ⇒ very-false
This is a variant of
ifwhere there are no else-forms, and possibly several then-forms. In particular,(when condition a b c)is entirely equivalent to
(if condition (progn a b c) nil)
This is a variant of
ifwhere there is no then-form:(unless condition a b c)is entirely equivalent to
(if condition nil a b c)
condchooses among an arbitrary number of alternatives. Each clause in thecondmust be a list. The car of this list is the condition; the remaining elements, if any, the body-forms. Thus, a clause looks like this:(condition body-forms...)
condtries the clauses in textual order, by evaluating the condition of each clause. If the value of condition is non-nil, the clause “succeeds”; thencondevaluates its body-forms, and the value of the last of body-forms becomes the value of thecond. The remaining clauses are ignored.If the value of condition is
nil, the clause “fails,” so thecondmoves on to the following clause, trying its condition.If every condition evaluates to
nil, so that every clause fails,condreturnsnil.A clause may also look like this:
(condition)Then, if condition is non-
nilwhen tested, the value of condition becomes the value of thecondform.The following example has four clauses, which test for the cases where the value of
xis a number, string, buffer and symbol, respectively:(cond ((numberp x) x) ((stringp x) x) ((bufferp x) (setq temporary-hack x) ; multiple body-forms (buffer-name x)) ; in one clause ((symbolp x) (symbol-value x)))Often we want to execute the last clause whenever none of the previous clauses was successful. To do this, we use
tas the condition of the last clause, like this:(tbody-forms). The formtevaluates tot, which is nevernil, so this clause never fails, provided thecondgets to it at all.For example,
(setq a 5) (cond ((eq a 'hack) 'foo) (t "default")) ⇒ "default"This
condexpression returnsfooif the value ofaishack, and returns the string"default"otherwise.
Any conditional construct can be expressed with cond or with
if. Therefore, the choice between them is a matter of style.
For example:
(if a b c)
==
(cond (a b) (t c))
This section describes three constructs that are often used together
with if and cond to express complicated conditions. The
constructs and and or can also be used individually as
kinds of multiple conditional constructs.
This function tests for the falsehood of condition. It returns
tif condition isnil, andnilotherwise. The functionnotis identical tonull, and we recommend using the namenullif you are testing for an empty list.
The
andspecial form tests whether all the conditions are true. It works by evaluating the conditions one by one in the order written.If any of the conditions evaluates to
nil, then the result of theandmust benilregardless of the remaining conditions; soandreturnsnilright away, ignoring the remaining conditions.If all the conditions turn out non-
nil, then the value of the last of them becomes the value of theandform. Just(and), with no conditions, returnst, appropriate because all the conditions turned out non-nil. (Think about it; which one did not?)Here is an example. The first condition returns the integer 1, which is not
nil. Similarly, the second condition returns the integer 2, which is notnil. The third condition isnil, so the remaining condition is never evaluated.(and (print 1) (print 2) nil (print 3)) -| 1 -| 2 ⇒ nilHere is a more realistic example of using
and:(if (and (consp foo) (eq (car foo) 'x)) (message "foo is a list starting with x"))Note that
(car foo)is not executed if(consp foo)returnsnil, thus avoiding an error.
andexpressions can also be written using eitheriforcond. Here's how:(and arg1 arg2 arg3) == (if arg1 (if arg2 arg3)) == (cond (arg1 (cond (arg2 arg3))))
The
orspecial form tests whether at least one of the conditions is true. It works by evaluating all the conditions one by one in the order written.If any of the conditions evaluates to a non-
nilvalue, then the result of theormust be non-nil; soorreturns right away, ignoring the remaining conditions. The value it returns is the non-nilvalue of the condition just evaluated.If all the conditions turn out
nil, then theorexpression returnsnil. Just(or), with no conditions, returnsnil, appropriate because all the conditions turned outnil. (Think about it; which one did not?)For example, this expression tests whether
xis eithernilor the integer zero:(or (eq x nil) (eq x 0))Like the
andconstruct,orcan be written in terms ofcond. For example:(or arg1 arg2 arg3) == (cond (arg1) (arg2) (arg3))You could almost write
orin terms ofif, but not quite:(if arg1 arg1 (if arg2 arg2 arg3))This is not completely equivalent because it can evaluate arg1 or arg2 twice. By contrast,
(orarg1 arg2 arg3)never evaluates any argument more than once.
Iteration means executing part of a program repetitively. For
example, you might want to repeat some computation once for each element
of a list, or once for each integer from 0 to n. You can do this
in Emacs Lisp with the special form while:
whilefirst evaluates condition. If the result is non-nil, it evaluates forms in textual order. Then it reevaluates condition, and if the result is non-nil, it evaluates forms again. This process repeats until condition evaluates tonil.There is no limit on the number of iterations that may occur. The loop will continue until either condition evaluates to
nilor until an error orthrowjumps out of it (see Nonlocal Exits).The value of a
whileform is alwaysnil.(setq num 0) ⇒ 0 (while (< num 4) (princ (format "Iteration %d." num)) (setq num (1+ num))) -| Iteration 0. -| Iteration 1. -| Iteration 2. -| Iteration 3. ⇒ nilTo write a “repeat...until” loop, which will execute something on each iteration and then do the end-test, put the body followed by the end-test in a
prognas the first argument ofwhile, as shown here:(while (progn (forward-line 1) (not (looking-at "^$"))))This moves forward one line and continues moving by lines until it reaches an empty line. It is peculiar in that the
whilehas no body, just the end test (which also does the real work of moving point).
The dolist and dotimes macros provide convenient ways to
write two common kinds of loops.
This construct executes body once for each element of list, binding the variable var locally to hold the current element. Then it returns the value of evaluating result, or
nilif result is omitted. For example, here is how you could usedolistto define thereversefunction:(defun reverse (list) (let (value) (dolist (elt list value) (setq value (cons elt value)))))
This construct executes body once for each integer from 0 (inclusive) to count (exclusive), binding the variable var to the integer for the current iteration. Then it returns the value of evaluating result, or
nilif result is omitted. Here is an example of usingdotimesto do something 100 times:(dotimes (i 100) (insert "I will not obey absurd orders\n"))
A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited.
catch and throwMost control constructs affect only the flow of control within the
construct itself. The function throw is the exception to this
rule of normal program execution: it performs a nonlocal exit on
request. (There are other exceptions, but they are for error handling
only.) throw is used inside a catch, and jumps back to
that catch. For example:
(defun foo-outer ()
(catch 'foo
(foo-inner)))
(defun foo-inner ()
...
(if x
(throw 'foo t))
...)
The throw form, if executed, transfers control straight back to
the corresponding catch, which returns immediately. The code
following the throw is not executed. The second argument of
throw is used as the return value of the catch.
The function throw finds the matching catch based on the
first argument: it searches for a catch whose first argument is
eq to the one specified in the throw. If there is more
than one applicable catch, the innermost one takes precedence.
Thus, in the above example, the throw specifies foo, and
the catch in foo-outer specifies the same symbol, so that
catch is the applicable one (assuming there is no other matching
catch in between).
Executing throw exits all Lisp constructs up to the matching
catch, including function calls. When binding constructs such as
let or function calls are exited in this way, the bindings are
unbound, just as they are when these constructs exit normally
(see Local Variables). Likewise, throw restores the buffer
and position saved by save-excursion (see Excursions), and
the narrowing status saved by save-restriction and the window
selection saved by save-window-excursion (see Window Configurations). It also runs any cleanups established with the
unwind-protect special form when it exits that form
(see Cleanups).
The throw need not appear lexically within the catch
that it jumps to. It can equally well be called from another function
called within the catch. As long as the throw takes place
chronologically after entry to the catch, and chronologically
before exit from it, it has access to that catch. This is why
throw can be used in commands such as exit-recursive-edit
that throw back to the editor command loop (see Recursive Editing).
Common Lisp note: Most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially:return,return-from, andgo, for example. Emacs Lisp has onlythrow.
catchestablishes a return point for thethrowfunction. The return point is distinguished from other such return points by tag, which may be any Lisp object exceptnil. The argument tag is evaluated normally before the return point is established.With the return point in effect,
catchevaluates the forms of the body in textual order. If the forms execute normally (without error or nonlocal exit) the value of the last body form is returned from thecatch.If a
throwis executed during the execution of body, specifying the same value tag, thecatchform exits immediately; the value it returns is whatever was specified as the second argument ofthrow.
The purpose of
throwis to return from a return point previously established withcatch. The argument tag is used to choose among the various existing return points; it must beeqto the value specified in thecatch. If multiple return points match tag, the innermost one is used.The argument value is used as the value to return from that
catch.If no return point is in effect with tag tag, then a
no-catcherror is signaled with data(tag value).
catch and throwOne way to use catch and throw is to exit from a doubly
nested loop. (In most languages, this would be done with a “go to.”)
Here we compute (foo i j) for i and j
varying from 0 to 9:
(defun search-foo ()
(catch 'loop
(let ((i 0))
(while (< i 10)
(let ((j 0))
(while (< j 10)
(if (foo i j)
(throw 'loop (list i j)))
(setq j (1+ j))))
(setq i (1+ i))))))
If foo ever returns non-nil, we stop immediately and return a
list of i and j. If foo always returns nil, the
catch returns normally, and the value is nil, since that
is the result of the while.
Here are two tricky examples, slightly different, showing two
return points at once. First, two return points with the same tag,
hack:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
⇒ catch2
(catch 'hack
(print (catch2 'hack))
'no)
-| yes
⇒ no
Since both return points have tags that match the throw, it goes to
the inner one, the one established in catch2. Therefore,
catch2 returns normally with value yes, and this value is
printed. Finally the second body form in the outer catch, which is
'no, is evaluated and returned from the outer catch.
Now let's change the argument given to catch2:
(catch 'hack
(print (catch2 'quux))
'no)
⇒ yes
We still have two return points, but this time only the outer one has
the tag hack; the inner one has the tag quux instead.
Therefore, throw makes the outer catch return the value
yes. The function print is never called, and the
body-form 'no is never evaluated.
When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error.
When an error is signaled, Emacs's default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer.
In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers that should be deleted before
the program is finished. In such cases, you would use
unwind-protect to establish cleanup expressions to be
evaluated in case of error. (See Cleanups.) Occasionally, you may
wish the program to continue execution despite an error in a subroutine.
In these cases, you would use condition-case to establish
error handlers to recover control in case of error.
Resist the temptation to use error handling to transfer control from
one part of the program to another; use catch and throw
instead. See Catch and Throw.
Signaling an error means beginning error processing. Error processing normally aborts all or part of the running program and returns to a point that is set up to handle the error (see Processing of Errors). Here we describe how to signal an error.
Most errors are signaled “automatically” within Lisp primitives
which you call for other purposes, such as if you try to take the
car of an integer or move forward a character at the end of the
buffer. You can also signal errors explicitly with the functions
error and signal.
Quitting, which happens when the user types C-g, is not considered an error, but it is handled almost like an error. See Quitting.
Every error specifies an error message, one way or another. The message should state what is wrong (“File does not exist”), not how things ought to be (“File must exist”). The convention in Emacs Lisp is that error messages should start with a capital letter, but should not end with any sort of punctuation.
This function signals an error with an error message constructed by applying
format(see Formatting Strings) to format-string and args.These examples show typical uses of
error:(error "That is an error -- try something else") error--> That is an error -- try something else (error "You have committed %d errors" 10) error--> You have committed 10 errors
errorworks by callingsignalwith two arguments: the error symbolerror, and a list containing the string returned byformat.Warning: If you want to use your own string as an error message verbatim, don't just write
(errorstring). If string contains ‘%’, it will be interpreted as a format specifier, with undesirable results. Instead, use(error "%s"string).
This function signals an error named by error-symbol. The argument data is a list of additional Lisp objects relevant to the circumstances of the error.
The argument error-symbol must be an error symbol—a symbol bearing a property
error-conditionswhose value is a list of condition names. This is how Emacs Lisp classifies different sorts of errors. See Error Symbols, for a description of error symbols, error conditions and condition names.If the error is not handled, the two arguments are used in printing the error message. Normally, this error message is provided by the
error-messageproperty of error-symbol. If data is non-nil, this is followed by a colon and a comma separated list of the unevaluated elements of data. Forerror, the error message is the car of data (that must be a string). Subcategories offile-errorare handled specially.The number and significance of the objects in data depends on error-symbol. For example, with a
wrong-type-argumenterror, there should be two objects in the list: a predicate that describes the type that was expected, and the object that failed to fit that type.Both error-symbol and data are available to any error handlers that handle the error:
condition-casebinds a local variable to a list of the form(error-symbol.data)(see Handling Errors).The function
signalnever returns (though in older Emacs versions it could sometimes return).(signal 'wrong-number-of-arguments '(x y)) error--> Wrong number of arguments: x, y (signal 'no-such-error '("My unknown error condition")) error--> peculiar error: "My unknown error condition"
Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors.
When an error is signaled, signal searches for an active
handler for the error. A handler is a sequence of Lisp
expressions designated to be executed if an error happens in part of the
Lisp program. If the error has an applicable handler, the handler is
executed, and control resumes following the handler. The handler
executes in the environment of the condition-case that
established it; all functions called within that condition-case
have already been exited, and the handler cannot return to them.
If there is no applicable handler for the error, it terminates the
current command and returns control to the editor command loop. (The
command loop has an implicit handler for all kinds of errors.) The
command loop's handler uses the error symbol and associated data to
print an error message. You can use the variable
command-error-function to control how this is done:
This variable, if non-
nil, specifies a function to use to handle errors that return control to the Emacs command loop. The function should take three arguments: data, a list of the same form thatcondition-casewould bind to its variable; context, a string describing the situation in which the error occurred, or (more often)nil; and caller, the Lisp function which called the primitive that signaled the error.
An error that has no explicit handler may call the Lisp debugger. The
debugger is enabled if the variable debug-on-error (see Error Debugging) is non-nil. Unlike error handlers, the debugger runs
in the environment of the error, so that you can examine values of
variables precisely as they were at the time of the error.
The usual effect of signaling an error is to terminate the command
that is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler, with the special form
condition-case. A simple example looks like this:
(condition-case nil
(delete-file filename)
(error nil))
This deletes the file named filename, catching any error and
returning nil if an error occurs4.
The condition-case construct is often used to trap errors that
are predictable, such as failure to open a file in a call to
insert-file-contents. It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.
The second argument of condition-case is called the
protected form. (In the example above, the protected form is a
call to delete-file.) The error handlers go into effect when
this form begins execution and are deactivated when this form returns.
They remain in effect for all the intervening time. In particular, they
are in effect during the execution of functions called by this form, in
their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
signal and error) called by the protected form, not by the
protected form itself.
The arguments after the protected form are handlers. Each handler
lists one or more condition names (which are symbols) to specify
which errors it will handle. The error symbol specified when an error
is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example
above, there is one handler, and it specifies one condition name,
error, which covers all errors.
The search for an applicable handler checks all the established handlers
starting with the most recently established one. Thus, if two nested
condition-case forms offer to handle the same error, the inner of
the two gets to handle it.
If an error is handled by some condition-case form, this
ordinarily prevents the debugger from being run, even if
debug-on-error says this error should invoke the debugger.
If you want to be able to debug errors that are caught by a
condition-case, set the variable debug-on-signal to a
non-nil value. You can also specify that a particular handler
should let the debugger run first, by writing debug among the
conditions, like this:
(condition-case nil
(delete-file filename)
((debug error) nil))
The effect of debug here is only to prevent
condition-case from suppressing the call to the debugger. Any
given error will invoke the debugger only if debug-on-error and
the other usual filtering mechanisms say it should. See Error Debugging.
Once Emacs decides that a certain handler handles the error, it
returns control to that handler. To do so, Emacs unbinds all variable
bindings made by binding constructs that are being exited, and
executes the cleanups of all unwind-protect forms that are
being exited. Once control arrives at the handler, the body of the
handler executes normally.
After execution of the handler body, execution returns from the
condition-case form. Because the protected form is exited
completely before execution of the handler, the handler cannot resume
execution at the point of the error, nor can it examine variable
bindings that were made within the protected form. All it can do is
clean up and proceed.
Error signaling and handling have some resemblance to throw and
catch (see Catch and Throw), but they are entirely separate
facilities. An error cannot be caught by a catch, and a
throw cannot be handled by an error handler (though using
throw when there is no suitable catch signals an error
that can be handled).
This special form establishes the error handlers handlers around the execution of protected-form. If protected-form executes without error, the value it returns becomes the value of the
condition-caseform; in this case, thecondition-casehas no effect. Thecondition-caseform makes a difference when an error occurs during protected-form.Each of the handlers is a list of the form
(conditions body...). Here conditions is an error condition name to be handled, or a list of condition names (which can includedebugto allow the debugger to run before the handler); body is one or more Lisp expressions to be executed when this handler handles an error. Here are examples of handlers:(error nil) (arith-error (message "Division by zero")) ((arith-error file-error) (message "Either division by zero or failure to open a file"))Each error that occurs has an error symbol that describes what kind of error it is. The
error-conditionsproperty of this symbol is a list of condition names (see Error Symbols). Emacs searches all the activecondition-caseforms for a handler that specifies one or more of these condition names; the innermost matchingcondition-casehandles the error. Within thiscondition-case, the first applicable handler handles the error.After executing the body of the handler, the
condition-casereturns normally, using the value of the last form in the handler body as the overall value.The argument var is a variable.
condition-casedoes not bind this variable when executing the protected-form, only when it handles an error. At that time, it binds var locally to an error description, which is a list giving the particulars of the error. The error description has the form(error-symbol.data). The handler can refer to this list to decide what to do. For example, if the error is for failure opening a file, the file name is the second element of data—the third element of the error description.If var is
nil, that means no variable is bound. Then the error symbol and associated data are not available to the handler.Sometimes it is necessary to re-throw a signal caught by
condition-case, for some outer-level handler to catch. Here's how to do that:(signal (car err) (cdr err))where
erris the error description variable, the first argument tocondition-casewhose error condition you want to re-throw. See Definition of signal.
This function returns the error message string for a given error descriptor. It is useful if you want to handle an error by printing the usual error message for that error. See Definition of signal.
Here is an example of using condition-case to handle the error
that results from dividing by zero. The handler displays the error
message (but without a beep), then returns a very large number.
(defun safe-divide (dividend divisor)
(condition-case err
;; Protected form.
(/ dividend divisor)
;; The handler.
(arith-error ; Condition.
;; Display the usual message for this error.
(message "%s" (error-message-string err))
1000000)))
⇒ safe-divide
(safe-divide 5 0)
-| Arithmetic error: (arith-error)
⇒ 1000000
The handler specifies condition name arith-error so that it will handle only division-by-zero errors. Other kinds of errors will not be handled, at least not by this condition-case. Thus,
(safe-divide nil 3)
error--> Wrong type argument: number-or-marker-p, nil
Here is a condition-case that catches all kinds of errors,
including those signaled with error:
(setq baz 34)
⇒ 34
(condition-case err
(if (eq baz 35)
t
;; This is a call to the function error.
(error "Rats! The variable %s was %s, not 35" 'baz baz))
;; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))
2))
-| The error was: (error "Rats! The variable baz was 34, not 35")
⇒ 2
This construct executes body, ignoring any errors that occur during its execution. If the execution is without error,
ignore-errorsreturns the value of the last form in body; otherwise, it returnsnil.Here's the example at the beginning of this subsection rewritten using
ignore-errors:(ignore-errors (delete-file filename))
When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Emacs Lisp language.
These narrow classifications are grouped into a hierarchy of wider
classes called error conditions, identified by condition
names. The narrowest such classes belong to the error symbols
themselves: each error symbol is also a condition name. There are also
condition names for more extensive classes, up to the condition name
error which takes in all kinds of errors (but not quit).
Thus, each error has one or more condition names: error, the
error symbol if that is distinct from error, and perhaps some
intermediate classifications.
In order for a symbol to be an error symbol, it must have an
error-conditions property which gives a list of condition names.
This list defines the conditions that this kind of error belongs to.
(The error symbol itself, and the symbol error, should always be
members of this list.) Thus, the hierarchy of condition names is
defined by the error-conditions properties of the error symbols.
Because quitting is not considered an error, the value of the
error-conditions property of quit is just (quit).
In addition to the error-conditions list, the error symbol
should have an error-message property whose value is a string to
be printed when that error is signaled but not handled. If the
error symbol has no error-message property or if the
error-message property exists, but is not a string, the error
message ‘peculiar error’ is used. See Definition of signal.
Here is how we define a new error symbol, new-error:
(put 'new-error
'error-conditions
'(error my-own-errors new-error))
⇒ (error my-own-errors new-error)
(put 'new-error 'error-message "A new error")
⇒ "A new error"
This error has three condition names: new-error, the narrowest
classification; my-own-errors, which we imagine is a wider
classification; and error, which is the widest of all.
The error string should start with a capital letter but it should not end with a period. This is for consistency with the rest of Emacs.
Naturally, Emacs will never signal new-error on its own; only
an explicit call to signal (see Definition of signal) in
your code can do this:
(signal 'new-error '(x y))
error--> A new error: x, y
This error can be handled through any of the three condition names.
This example handles new-error and any other errors in the class
my-own-errors:
(condition-case foo
(bar nil t)
(my-own-errors nil))
The significant way that errors are classified is by their condition
names—the names used to match errors with handlers. An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names. It would be cumbersome to give
signal a list of condition names rather than one error symbol.
By contrast, using only error symbols without condition names would
seriously decrease the power of condition-case. Condition names
make it possible to categorize errors at various levels of generality
when you write an error handler. Using error symbols alone would
eliminate all but the narrowest level of classification.
See Standard Errors, for a list of all the standard error symbols and their conditions.
The unwind-protect construct is essential whenever you
temporarily put a data structure in an inconsistent state; it permits
you to make the data consistent again in the event of an error or
throw. (Another more specific cleanup construct that is used only for
changes in buffer contents is the atomic change group; Atomic Changes.)
unwind-protectexecutes body-form with a guarantee that the cleanup-forms will be evaluated if control leaves body-form, no matter how that happens. body-form may complete normally, or execute athrowout of theunwind-protect, or cause an error; in all cases, the cleanup-forms will be evaluated.If body-form finishes normally,
unwind-protectreturns the value of body-form, after it evaluates the cleanup-forms. If body-form does not finish,unwind-protectdoes not return any value in the normal sense.Only body-form is protected by the
unwind-protect. If any of the cleanup-forms themselves exits nonlocally (via athrowor an error),unwind-protectis not guaranteed to evaluate the rest of them. If the failure of one of the cleanup-forms has the potential to cause trouble, then protect it with anotherunwind-protectaround that form.The number of currently active
unwind-protectforms counts, together with the number of local variable bindings, against the limitmax-specpdl-size(see Local Variables).
For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing:
(let ((buffer (get-buffer-create " *temp*")))
(with-current-buffer buffer
(unwind-protect
body-form
(kill-buffer buffer))))
You might think that we could just as well write (kill-buffer
(current-buffer)) and dispense with the variable buffer.
However, the way shown above is safer, if body-form happens to
get an error after switching to a different buffer! (Alternatively,
you could write a save-current-buffer around body-form,
to ensure that the temporary buffer becomes current again in time to
kill it.)
Emacs includes a standard macro called with-temp-buffer which
expands into more or less the code shown above (see Current Buffer). Several of the macros defined in
this manual use unwind-protect in this way.
Here is an actual example derived from an FTP package. It creates a
process (see Processes) to try to establish a connection to a remote
machine. As the function ftp-login is highly susceptible to
numerous problems that the writer of the function cannot anticipate, it
is protected with a form that guarantees deletion of the process in the
event of failure. Otherwise, Emacs might fill up with useless
subprocesses.
(let ((win nil))
(unwind-protect
(progn
(setq process (ftp-setup-buffer host file))
(if (setq win (ftp-login process host user password))
(message "Logged in")
(error "Ftp login failed")))
(or win (and process (delete-process process)))))
This example has a small bug: if the user types C-g to
quit, and the quit happens immediately after the function
ftp-setup-buffer returns but before the variable process is
set, the process will not be killed. There is no easy way to fix this bug,
but at least it is very unlikely.
A variable is a name used in a program to stand for a value. Nearly all programming languages have variables of some sort. In the text of a Lisp program, variables are written using the syntax for symbols.
In Lisp, unlike most programming languages, programs are represented primarily as Lisp objects and only secondarily as text. The Lisp objects used for variables are symbols: the symbol name is the variable name, and the variable's value is stored in the value cell of the symbol. The use of a symbol as a variable is independent of its use as a function name. See Symbol Components.
The textual form of a Lisp program is given by the read syntax of the Lisp objects that constitute the program. Hence, a variable in a textual Lisp program is written using the read syntax for the symbol representing the variable.
The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq. For example,
(setq x '(a b))
gives the variable x the value (a b). Note that
setq is a special form (see Special Forms); it does not
evaluate its first argument, the name of the variable, but it does
evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the symbol itself as an expression. Thus,
x ⇒ (a b)
assuming the setq form shown above has already been executed.
If you do set the same variable again, the new value replaces the old one:
x
⇒ (a b)
(setq x 4)
⇒ 4
x
⇒ 4
In Emacs Lisp, certain symbols normally evaluate to themselves. These
include nil and t, as well as any symbol whose name starts
with ‘:’ (these are called keywords). These symbols cannot
be rebound, nor can their values be changed. Any attempt to set or bind
nil or t signals a setting-constant error. The
same is true for a keyword (a symbol whose name starts with ‘:’),
if it is interned in the standard obarray, except that setting such a
symbol to itself is not an error.
nil == 'nil
⇒ nil
(setq nil 500)
error--> Attempt to set constant symbol: nil
function returns
tif object is a symbol whose name starts with ‘:’, interned in the standard obarray, and returnsnilotherwise.
These constants are fundamentally different from the “constants”
defined using the defconst special form (see Defining Variables). A defconst form serves to inform human readers
that you do not intend to change the value of a variable, but Emacs
does not raise an error if you actually change it.
Global variables have values that last until explicitly superseded with new values. Sometimes it is useful to create variable values that exist temporarily—only until a certain part of the program finishes. These values are called local, and the variables so used are called local variables.
For example, when a function is called, its argument variables receive
new local values that last until the function exits. The let
special form explicitly establishes new local values for specified
variables; these last until exit from the let form.
Establishing a local value saves away the variable's previous value (or lack of one). We say that the previous value is shadowed and not visible. Both global and local values may be shadowed (see Scope). After the life span of the local value is over, the previous value (or lack of one) is restored.
If you set a variable (such as with setq) while it is local,
this replaces the local value; it does not alter the global value, or
previous local values, that are shadowed. To model this behavior, we
speak of a local binding of the variable as well as a local value.
The local binding is a conceptual place that holds a local value.
Entering a function, or a special form such as let, creates the
local binding; exiting the function or the let removes the
local binding. While the local binding lasts, the variable's value is
stored within it. Using setq or set while there is a
local binding stores a different value into the local binding; it does
not create a new binding.
We also speak of the global binding, which is where (conceptually) the global value is kept.
A variable can have more than one local binding at a time (for
example, if there are nested let forms that bind it). In such a
case, the most recently created local binding that still exists is the
current binding of the variable. (This rule is called
dynamic scoping; see Variable Scoping.) If there are no
local bindings, the variable's global binding is its current binding.
We sometimes call the current binding the most-local existing
binding, for emphasis. Ordinary evaluation of a symbol always returns
the value of its current binding.
The special forms let and let* exist to create
local bindings.
This special form binds variables according to bindings and then evaluates all of the forms in textual order. The
let-form returns the value of the last form in forms.Each of the bindings is either (i) a symbol, in which case that symbol is bound to
nil; or (ii) a list of the form(symbol value-form), in which case symbol is bound to the result of evaluating value-form. If value-form is omitted,nilis used.All of the value-forms in bindings are evaluated in the order they appear and before binding any of the symbols to them. Here is an example of this:
zis bound to the old value ofy, which is 2, not the new value ofy, which is 1.(setq y 2) ⇒ 2 (let ((y 1) (z y)) (list y z)) ⇒ (1 2)
This special form is like
let, but it binds each variable right after computing its local value, before computing the local value for the next variable. Therefore, an expression in bindings can reasonably refer to the preceding symbols bound in thislet*form. Compare the following example with the example above forlet.(setq y 2) ⇒ 2 (let* ((y 1) (z y)) ; Use the just-established value ofy. (list y z)) ⇒ (1 1)
Here is a complete list of the other facilities that create local bindings:
Variables can also have buffer-local bindings (see Buffer-Local Variables); a few variables have terminal-local bindings (see Multiple Terminals). These kinds of bindings work somewhat like ordinary local bindings, but they are localized depending on “where” you are in Emacs, rather than localized in time.
This variable defines the limit on the total number of local variable bindings and
unwind-protectcleanups (see Cleaning Up from Nonlocal Exits) that are allowed before Emacs signals an error (with data"Variable binding depth exceeds max-specpdl-size").This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.
max-lisp-eval-depthprovides another limit on depth of nesting. See Eval.The default value is 1000. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
If you have never given a symbol any value as a global variable, we
say that that symbol's global value is void. In other words, the
symbol's value cell does not have any Lisp object in it. If you try to
evaluate the symbol, you get a void-variable error rather than
a value.
Note that a value of nil is not the same as void. The symbol
nil is a Lisp object and can be the value of a variable just as any
other object can be; but it is a value. A void variable does not
have any value.
After you have given a variable a value, you can make it void once more
using makunbound.
This function makes the current variable binding of symbol void. Subsequent attempts to use this symbol's value as a variable will signal the error
void-variable, unless and until you set it again.
makunboundreturns symbol.(makunbound 'x) ; Make the global value ofxvoid. ⇒ x x error--> Symbol's value as variable is void: xIf symbol is locally bound,
makunboundaffects the most local existing binding. This is the only way a symbol can have a void local binding, since all the constructs that create local bindings create them with values. In this case, the voidness lasts at most as long as the binding does; when the binding is removed due to exit from the construct that made it, the previous local or global binding is reexposed as usual, and the variable is no longer void unless the newly reexposed binding was void all along.(setq x 1) ; Put a value in the global binding. ⇒ 1 (let ((x 2)) ; Locally bind it. (makunbound 'x) ; Void the local binding. x) error--> Symbol's value as variable is void: x x ; The global binding is unchanged. ⇒ 1 (let ((x 2)) ; Locally bind it. (let ((x 3)) ; And again. (makunbound 'x) ; Void the innermost-local binding. x)) ; And refer: it's void. error--> Symbol's value as variable is void: x (let ((x 2)) (let ((x 3)) (makunbound 'x)) ; Void inner binding, then remove it. x) ; Now outerletbinding is visible. ⇒ 2
A variable that has been made void with makunbound is
indistinguishable from one that has never received a value and has
always been void.
You can use the function boundp to test whether a variable is
currently void.
boundpreturnstif variable (a symbol) is not void; more precisely, if its current binding is not void. It returnsnilotherwise.(boundp 'abracadabra) ; Starts out void. ⇒ nil (let ((abracadabra 5)) ; Locally bind it. (boundp 'abracadabra)) ⇒ t (boundp 'abracadabra) ; Still globally void. ⇒ nil (setq abracadabra 5) ; Make it globally nonvoid. ⇒ 5 (boundp 'abracadabra) ⇒ t
You may announce your intention to use a symbol as a global variable
with a variable definition: a special form, either defconst
or defvar.
In Emacs Lisp, definitions serve three purposes. First, they inform
people who read the code that certain symbols are intended to be
used a certain way (as variables). Second, they inform the Lisp system
of these things, supplying a value and documentation. Third, they
provide information to utilities such as etags and
make-docfile, which create data bases of the functions and
variables in a program.
The difference between defconst and defvar is primarily
a matter of intent, serving to inform human readers of whether the value
should ever change. Emacs Lisp does not restrict the ways in which a
variable can be used based on defconst or defvar
declarations. However, it does make a difference for initialization:
defconst unconditionally initializes the variable, while
defvar initializes it only if it is void.
This special form defines symbol as a variable and can also initialize and document it. The definition informs a person reading your code that symbol is used as a variable that might be set or changed. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the
defvar.If symbol is void and value is specified,
defvarevaluates it and sets symbol to the result. But if symbol already has a value (i.e., it is not void), value is not even evaluated, and symbol's value remains unchanged. If value is omitted, the value of symbol is not changed in any case.If symbol has a buffer-local binding in the current buffer,
defvaroperates on the default value, which is buffer-independent, not the current (buffer-local) binding. It sets the default value if the default value is void. See Buffer-Local Variables.When you evaluate a top-level
defvarform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunarranges to set the variable unconditionally, without testing whether its value is void.If the doc-string argument appears, it specifies the documentation for the variable. (This opportunity to specify documentation is one of the main benefits of defining the variable.) The documentation is stored in the symbol's
variable-documentationproperty. The Emacs help functions (see Documentation) look for this property.If the documentation string begins with the character ‘*’, Emacs allows users to set it interactively using the
set-variablecommand. However, you should nearly always usedefcustominstead ofdefvarto define such variables, so that users can use M-x customize and related commands to set them. In that case, it is not necessary to begin the documentation string with ‘*’. See Customization.Here are some examples. This form defines
foobut does not initialize it:(defvar foo) ⇒ fooThis example initializes the value of
barto23, and gives it a documentation string:(defvar bar 23 "The normal weight of a bar.") ⇒ barThe following form changes the documentation string for
bar, making it a user option, but does not change the value, sincebaralready has a value. (The addition(1+ nil)would get an error if it were evaluated, but since it is not evaluated, there is no error.)(defvar bar (1+ nil) "*The normal weight of a bar.") ⇒ bar bar ⇒ 23Here is an equivalent expression for the
defvarspecial form:(defvar symbol value doc-string) == (progn (if (not (boundp 'symbol)) (setq symbol value)) (if 'doc-string (put 'symbol 'variable-documentation 'doc-string)) 'symbol)The
defvarform returns symbol, but it is normally used at top level in a file where its value does not matter.
This special form defines symbol as a value and initializes it. It informs a person reading your code that symbol has a standard global value, established here, that should not be changed by the user or by other programs. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the
defconst.
defconstalways evaluates value, and sets the value of symbol to the result. If symbol does have a buffer-local binding in the current buffer,defconstsets the default value, not the buffer-local value. (But you should not be making buffer-local bindings for a symbol that is defined withdefconst.)An example of the use of
defconstis Emacs' definition offloat-pi—the mathematical constant pi, which ought not to be changed by anyone (attempts by the Indiana State Legislature notwithstanding). As the second form illustrates, however,defconstis only advisory.(defconst float-pi 3.141592653589793 "The value of Pi.") ⇒ float-pi (setq float-pi 3) ⇒ float-pi float-pi ⇒ 3
This function returns
tif variable is a user option—a variable intended to be set by the user for customization—andnilotherwise. (Variables other than user options exist for the internal purposes of Lisp programs, and users need not know about them.)User option variables are distinguished from other variables either though being declared using
defcustom5 or by the first character of theirvariable-documentationproperty. If the property exists and is a string, and its first character is ‘*’, then the variable is a user option. Aliases of user options are also user options.
If a user option variable has a variable-interactive property,
the set-variable command uses that value to control reading the
new value for the variable. The property's value is used as if it were
specified in interactive (see Using Interactive). However,
this feature is largely obsoleted by defcustom
(see Customization).
Warning: If the defconst and defvar special
forms are used while the variable has a local binding (made with
let, or a function argument), they set the local-binding's
value; the top-level binding is not changed. This is not what you
usually want. To prevent it, use these special forms at top level in
a file, where normally no local binding is in effect, and make sure to
load the file before making a local binding for the variable.
When you define a variable whose value is a function, or a list of functions, use a name that ends in ‘-function’ or ‘-functions’, respectively.
There are several other variable name conventions; here is a complete list:
nil for “good” arguments and nil for “bad”
arguments.
nil or not.
Since such variables often end up acquiring more values over time,
this convention is not strongly recommended.
When you define a variable, always consider whether you should mark it as “safe” or “risky”; see File Local Variables.
When defining and initializing a variable that holds a complicated
value (such as a keymap with bindings in it), it's best to put the
entire computation of the value into the defvar, like this:
(defvar my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
map)
docstring)
This method has several benefits. First, if the user quits while
loading the file, the variable is either still uninitialized or
initialized properly, never in-between. If it is still uninitialized,
reloading the file will initialize it properly. Second, reloading the
file once the variable is initialized will not alter it; that is
important if the user has run hooks to alter part of the contents (such
as, to rebind keys). Third, evaluating the defvar form with
C-M-x will reinitialize the map completely.
Putting so much code in the defvar form has one disadvantage:
it puts the documentation string far away from the line which names the
variable. Here's a safe way to avoid that:
(defvar my-mode-map nil
docstring)
(unless my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
(setq my-mode-map map)))
This has all the same advantages as putting the initialization inside
the defvar, except that you must type C-M-x twice, once on
each form, if you do want to reinitialize the variable.
But be careful not to write the code like this:
(defvar my-mode-map nil
docstring)
(unless my-mode-map
(setq my-mode-map (make-sparse-keymap))
(define-key my-mode-map "\C-c\C-a" 'my-command)
...)
This code sets the variable, then alters it, but it does so in more than
one step. If the user quits just after the setq, that leaves the
variable neither correctly initialized nor void nor nil. Once
that happens, reloading the file will not initialize the variable; it
will remain incomplete.
The usual way to reference a variable is to write the symbol which
names it (see Symbol Forms). This requires you to specify the
variable name when you write the program. Usually that is exactly what
you want to do. Occasionally you need to choose at run time which
variable to reference; then you can use symbol-value.
This function returns the value of symbol. This is the value in the innermost local binding of the symbol, or its global value if it has no local bindings.
(setq abracadabra 5) ⇒ 5 (setq foo 9) ⇒ 9 ;; Here the symbolabracadabra;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value 'abracadabra)) ⇒ foo ;; Here, the value ofabracadabra, ;; which isfoo, ;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value abracadabra)) ⇒ 9 (symbol-value 'abracadabra) ⇒ 5A
void-variableerror is signaled if the current binding of symbol is void.
The usual way to change the value of a variable is with the special
form setq. When you need to compute the choice of variable at
run time, use the function set.
This special form is the most common method of changing a variable's value. Each symbol is given a new value, which is the result of evaluating the corresponding form. The most-local existing binding of the symbol is changed.
setqdoes not evaluate symbol; it sets the symbol that you write. We say that this argument is automatically quoted. The ‘q’ insetqstands for “quoted.”The value of the
setqform is the value of the last form.(setq x (1+ 2)) ⇒ 3 x ;xnow has a global value. ⇒ 3 (let ((x 5)) (setq x 6) ; The local binding ofxis set. x) ⇒ 6 x ; The global value is unchanged. ⇒ 3Note that the first form is evaluated, then the first symbol is set, then the second form is evaluated, then the second symbol is set, and so on:
(setq x 10 ; Notice thatxis set before y (1+ x)) ; the value ofyis computed. ⇒ 11
This function sets symbol's value to value, then returns value. Since
setis a function, the expression written for symbol is evaluated to obtain the symbol to set.The most-local existing binding of the variable is the binding that is set; shadowed bindings are not affected.
(set one 1) error--> Symbol's value as variable is void: one (set 'one 1) ⇒ 1 (set 'two 'one) ⇒ one (set two 2) ;twoevaluates to symbolone. ⇒ 2 one ; So it isonethat was set. ⇒ 2 (let ((one 1)) ; This binding ofoneis set, (set 'one 3) ; not the global value. one) ⇒ 3 one ⇒ 2If symbol is not actually a symbol, a
wrong-type-argumenterror is signaled.(set '(x y) 'z) error--> Wrong type argument: symbolp, (x y)Logically speaking,
setis a more fundamental primitive thansetq. Any use ofsetqcan be trivially rewritten to useset;setqcould even be defined as a macro, given the availability ofset. However,setitself is rarely used; beginners hardly need to know about it. It is useful only for choosing at run time which variable to set. For example, the commandset-variable, which reads a variable name from the user and then sets the variable, needs to useset.Common Lisp note: In Common Lisp,setalways changes the symbol's “special” or dynamic value, ignoring any lexical bindings. In Emacs Lisp, all variables and all bindings are dynamic, sosetalways affects the most local existing binding.
A given symbol foo can have several local variable bindings,
established at different places in the Lisp program, as well as a global
binding. The most recently established binding takes precedence over
the others.
Local bindings in Emacs Lisp have indefinite scope and dynamic extent. Scope refers to where textually in the source code the binding can be accessed. “Indefinite scope” means that any part of the program can potentially access the variable binding. Extent refers to when, as the program is executing, the binding exists. “Dynamic extent” means that the binding lasts as long as the activation of the construct that established it.
The combination of dynamic extent and indefinite scope is called dynamic scoping. By contrast, most programming languages use lexical scoping, in which references to a local variable must be located textually within the function or block that binds the variable.
Common Lisp note: Variables declared “special” in Common Lisp are dynamically scoped, like all variables in Emacs Lisp.
Emacs Lisp uses indefinite scope for local variable bindings. This means that any function anywhere in the program text might access a given binding of a variable. Consider the following function definitions:
(defun binder (x) ;xis bound inbinder. (foo 5)) ;foois some other function. (defun user () ;xis used ``free'' inuser. (list x))
In a lexically scoped language, the binding of x in
binder would never be accessible in user, because
user is not textually contained within the function
binder. However, in dynamically-scoped Emacs Lisp, user
may or may not refer to the binding of x established in
binder, depending on the circumstances:
user directly without calling binder at all,
then whatever binding of x is found, it cannot come from
binder.
foo as follows and then call binder, then the
binding made in binder will be seen in user:
(defun foo (lose)
(user))
foo as follows and then call binder,
then the binding made in binder will not be seen in
user:
(defun foo (x)
(user))
Here, when foo is called by binder, it binds x.
(The binding in foo is said to shadow the one made in
binder.) Therefore, user will access the x bound
by foo instead of the one bound by binder.
Emacs Lisp uses dynamic scoping because simple implementations of lexical scoping are slow. In addition, every Lisp system needs to offer dynamic scoping at least as an option; if lexical scoping is the norm, there must be a way to specify dynamic scoping instead for a particular variable. It might not be a bad thing for Emacs to offer both, but implementing it with dynamic scoping only was much easier.
Extent refers to the time during program execution that a variable name is valid. In Emacs Lisp, a variable is valid only while the form that bound it is executing. This is called dynamic extent. “Local” or “automatic” variables in most languages, including C and Pascal, have dynamic extent.
One alternative to dynamic extent is indefinite extent. This means that a variable binding can live on past the exit from the form that made the binding. Common Lisp and Scheme, for example, support this, but Emacs Lisp does not.
To illustrate this, the function below, make-add, returns a
function that purports to add n to its own argument m. This
would work in Common Lisp, but it does not do the job in Emacs Lisp,
because after the call to make-add exits, the variable n
is no longer bound to the actual argument 2.
(defun make-add (n)
(function (lambda (m) (+ n m)))) ; Return a function.
⇒ make-add
(fset 'add2 (make-add 2)) ; Define function add2
; with (make-add 2).
⇒ (lambda (m) (+ n m))
(add2 4) ; Try to add 2 to 4.
error--> Symbol's value as variable is void: n
Some Lisp dialects have “closures,” objects that are like functions but record additional variable bindings. Emacs Lisp does not have closures.
A simple sample implementation (which is not how Emacs Lisp actually works) may help you understand dynamic binding. This technique is called deep binding and was used in early Lisp systems.
Suppose there is a stack of bindings, which are variable-value pairs.
At entry to a function or to a let form, we can push bindings
onto the stack for the arguments or local variables created there. We
can pop those bindings from the stack at exit from the binding
construct.
We can find the value of a variable by searching the stack from top to bottom for a binding for that variable; the value from that binding is the value of the variable. To set the variable, we search for the current binding, then store the new value into that binding.
As you can see, a function's bindings remain in effect as long as it continues execution, even during its calls to other functions. That is why we say the extent of the binding is dynamic. And any other function can refer to the bindings, if it uses the same variables while the bindings are in effect. That is why we say the scope is indefinite.
The actual implementation of variable scoping in GNU Emacs Lisp uses a technique called shallow binding. Each variable has a standard place in which its current value is always found—the value cell of the symbol.
In shallow binding, setting the variable works by storing a value in the value cell. Creating a new binding works by pushing the old value (belonging to a previous binding) onto a stack, and storing the new local value in the value cell. Eliminating a binding works by popping the old value off the stack, into the value cell.
We use shallow binding because it has the same results as deep binding, but runs faster, since there is never a need to search for a binding.
Binding a variable in one function and using it in another is a powerful technique, but if used without restraint, it can make programs hard to understand. There are two clean ways to use this technique:
You should write comments to inform other programmers that they can see all uses of the variable before them, and to advise them not to add uses elsewhere.
case-fold-search is defined as “non-nil means ignore case
when searching”; various search and replace functions refer to it
directly or through their subroutines, but do not bind or set it.
Then you can bind the variable in other programs, knowing reliably what the effect will be.
In either case, you should define the variable with defvar.
This helps other people understand your program by telling them to look
for inter-function usage. It also avoids a warning from the byte
compiler. Choose the variable's name to avoid name conflicts—don't
use short names like x.
Global and local variable bindings are found in most programming languages in one form or another. Emacs, however, also supports additional, unusual kinds of variable binding, such as buffer-local bindings, which apply only in one buffer. Having different values for a variable in different buffers is an important customization method. (Variables can also have bindings that are local to each terminal, or to each frame. See Multiple Terminals, and See Frame-Local Variables.)
A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so its other bindings are unchanged. This means that the change is visible only in the buffer where you made it.
The variable's ordinary binding, which is not associated with any specific buffer, is called the default binding. In most cases, this is the global binding.
A variable can have buffer-local bindings in some buffers but not in other buffers. The default binding is shared by all the buffers that don't have their own bindings for the variable. (This includes all newly-created buffers.) If you set the variable in a buffer that does not have a buffer-local binding for it, this sets the default binding, so the new value is visible in all the buffers that see the default binding.
The most common use of buffer-local bindings is for major modes to change
variables that control the behavior of commands. For example, C mode and
Lisp mode both set the variable paragraph-start to specify that only
blank lines separate paragraphs. They do this by making the variable
buffer-local in the buffer that is being put into C mode or Lisp mode, and
then setting it to the new value for that mode. See Major Modes.
The usual way to make a buffer-local binding is with
make-local-variable, which is what major mode commands typically
use. This affects just the current buffer; all other buffers (including
those yet to be created) will continue to share the default value unless
they are explicitly given their own buffer-local bindings.
A more powerful operation is to mark the variable as
automatically buffer-local by calling
make-variable-buffer-local. You can think of this as making the
variable local in all buffers, even those yet to be created. More
precisely, the effect is that setting the variable automatically makes
the variable local to the current buffer if it is not already so. All
buffers start out by sharing the default value of the variable as usual,
but setting the variable creates a buffer-local binding for the current
buffer. The new value is stored in the buffer-local binding, leaving
the default binding untouched. This means that the default value cannot
be changed with setq in any buffer; the only way to change it is
with setq-default.
Warning: When a variable has buffer-local
bindings in one or more buffers, let rebinds the binding that's
currently in effect. For instance, if the current buffer has a
buffer-local value, let temporarily rebinds that. If no
buffer-local bindings are in effect, let rebinds
the default value. If inside the let you then change to a
different current buffer in which a different binding is in effect,
you won't see the let binding any more. And if you exit the
let while still in the other buffer, you won't see the
unbinding occur (though it will occur properly). Here is an example
to illustrate:
(setq foo 'g)
(set-buffer "a")
(make-local-variable 'foo)
(setq foo 'a)
(let ((foo 'temp))
;; foo ⇒ 'temp ; let binding in buffer ‘a’
(set-buffer "b")
;; foo ⇒ 'g ; the global value since foo is not local in ‘b’
body...)
foo ⇒ 'g ; exiting restored the local value in buffer ‘a’,
; but we don't see that in buffer ‘b’
(set-buffer "a") ; verify the local value was restored
foo ⇒ 'a
Note that references to foo in body access the
buffer-local binding of buffer ‘b’.
When a file specifies local variable values, these become buffer-local values when you visit the file. See File Variables.
A buffer-local variable cannot be made frame-local (see Frame-Local Variables) or terminal-local (see Multiple Terminals).
This function creates a buffer-local binding in the current buffer for variable (a symbol). Other buffers are not affected. The value returned is variable.
The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.
;; In buffer ‘b1’: (setq foo 5) ; Affects all buffers. ⇒ 5 (make-local-variable 'foo) ; Now it is local in ‘b1’. ⇒ foo foo ; That did not change ⇒ 5 ; the value. (setq foo 6) ; Change the value ⇒ 6 ; in ‘b1’. foo ⇒ 6 ;; In buffer ‘b2’, the value hasn't changed. (with-current-buffer "b2" foo) ⇒ 5Making a variable buffer-local within a
let-binding for that variable does not work reliably, unless the buffer in which you do this is not current either on entry to or exit from thelet. This is becauseletdoes not distinguish between different kinds of bindings; it knows only which variable the binding was made for.If the variable is terminal-local (see Multiple Terminals), or frame-local (see Frame-Local Variables), this function signals an error. Such variables cannot have buffer-local bindings as well.
Warning: do not use
make-local-variablefor a hook variable. The hook variables are automatically made buffer-local as needed if you use the local argument toadd-hookorremove-hook.
This function marks variable (a symbol) automatically buffer-local, so that any subsequent attempt to set it will make it local to the current buffer at the time.
A peculiar wrinkle of this feature is that binding the variable (with
letor other binding constructs) does not create a buffer-local binding for it. Only setting the variable (withsetorsetq), while the variable does not have alet-style binding that was made in the current buffer, does so.If variable does not have a default value, then calling this command will give it a default value of
nil. If variable already has a default value, that value remains unchanged. Subsequently callingmakunboundon variable will result in a void buffer-local value and leave the default value unaffected.The value returned is variable.
Warning: Don't assume that you should use
make-variable-buffer-localfor user-option variables, simply because users might want to customize them differently in different buffers. Users can make any variable local, when they wish to. It is better to leave the choice to them.The time to use
make-variable-buffer-localis when it is crucial that no two buffers ever share the same binding. For example, when a variable is used for internal purposes in a Lisp program which depends on having separate values in separate buffers, then usingmake-variable-buffer-localcan be the best solution.
This returns
tif variable is buffer-local in buffer buffer (which defaults to the current buffer); otherwise,nil.
This returns
tif variable will become buffer-local in buffer buffer (which defaults to the current buffer) if it is set there.
This function returns the buffer-local binding of variable (a symbol) in buffer buffer. If variable does not have a buffer-local binding in buffer buffer, it returns the default value (see Default Value) of variable instead.
This function returns a list describing the buffer-local variables in buffer buffer. (If buffer is omitted, the current buffer is used.) It returns an association list (see Association Lists) in which each element contains one buffer-local variable and its value. However, when a variable's buffer-local binding in buffer is void, then the variable appears directly in the resulting list.
(make-local-variable 'foobar) (makunbound 'foobar) (make-local-variable 'bind-me) (setq bind-me 69) (setq lcl (buffer-local-variables)) ;; First, built-in variables local in all buffers: ⇒ ((mark-active . nil) (buffer-undo-list . nil) (mode-name . "Fundamental") ... ;; Next, non-built-in buffer-local variables. ;; This one is buffer-local and void: foobar ;; This one is buffer-local and nonvoid: (bind-me . 69))Note that storing new values into the cdrs of cons cells in this list does not change the buffer-local values of the variables.
This function deletes the buffer-local binding (if any) for variable (a symbol) in the current buffer. As a result, the default binding of variable becomes visible in this buffer. This typically results in a change in the value of variable, since the default value is usually different from the buffer-local value just eliminated.
If you kill the buffer-local binding of a variable that automatically becomes buffer-local when set, this makes the default value visible in the current buffer. However, if you set the variable again, that will once again create a buffer-local binding for it.
kill-local-variablereturns variable.This function is a command because it is sometimes useful to kill one buffer-local variable interactively, just as it is useful to create buffer-local variables interactively.
This function eliminates all the buffer-local variable bindings of the current buffer except for variables marked as “permanent” and local hook functions that have a non-
nilpermanent-local-hookproperty (see Setting Hooks). As a result, the buffer will see the default values of most variables.This function also resets certain other information pertaining to the buffer: it sets the local keymap to
nil, the syntax table to the value of(standard-syntax-table), the case table to(standard-case-table), and the abbrev table to the value offundamental-mode-abbrev-table.The very first thing this function does is run the normal hook
change-major-mode-hook(see below).Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.
kill-all-local-variablesreturnsnil.
The function
kill-all-local-variablesruns this normal hook before it does anything else. This gives major modes a way to arrange for something special to be done if the user switches to a different major mode. It is also useful for buffer-specific minor modes that should be forgotten if the user changes the major mode.For best results, make this variable buffer-local, so that it will disappear after doing its job and will not interfere with the subsequent major mode. See Hooks.
A buffer-local variable is permanent if the variable name (a
symbol) has a permanent-local property that is non-nil.
Such variables are unaffected by kill-all-local-variables, and
their local bindings are therefore not cleared by changing major modes.
Permanent locals are appropriate for data pertaining to where the file
came from or how to save it, rather than with how to edit the contents.
The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect whenever neither the current buffer nor the selected frame has its own binding for the variable.
The functions default-value and setq-default access and
change a variable's default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
setq-default to change the default setting of
paragraph-start for most buffers; and this would work even when
you are in a C or Lisp mode buffer that has a buffer-local value for
this variable.
The special forms defvar and defconst also set the
default value (if they set the variable at all), rather than any
buffer-local value.
This function returns symbol's default value. This is the value that is seen in buffers and frames that do not have their own values for this variable. If symbol is not buffer-local, this is equivalent to
symbol-value(see Accessing Variables).
The function
default-boundptells you whether symbol's default value is nonvoid. If(default-boundp 'foo)returnsnil, then(default-value 'foo)would get an error.
default-boundpis todefault-valueasboundpis tosymbol-value.
This special form gives each symbol a new default value, which is the result of evaluating the corresponding form. It does not evaluate symbol, but does evaluate form. The value of the
setq-defaultform is the value of the last form.If a symbol is not buffer-local for the current buffer, and is not marked automatically buffer-local,
setq-defaulthas the same effect assetq. If symbol is buffer-local for the current buffer, then this changes the value that other buffers will see (as long as they don't have a buffer-local value), but not the value that the current buffer sees.;; In buffer ‘foo’: (make-local-variable 'buffer-local) ⇒ buffer-local (setq buffer-local 'value-in-foo) ⇒ value-in-foo (setq-default buffer-local 'new-default) ⇒ new-default buffer-local ⇒ value-in-foo (default-value 'buffer-local) ⇒ new-default ;; In (the new) buffer ‘bar’: buffer-local ⇒ new-default (default-value 'buffer-local) ⇒ new-default (setq buffer-local 'another-default) ⇒ another-default (default-value 'buffer-local) ⇒ another-default ;; Back in buffer ‘foo’: buffer-local ⇒ value-in-foo (default-value 'buffer-local) ⇒ another-default
This function is like
setq-default, except that symbol is an ordinary evaluated argument.(set-default (car '(a b c)) 23) ⇒ 23 (default-value 'a) ⇒ 23
A file can specify local variable values; Emacs uses these to create buffer-local bindings for those variables in the buffer visiting that file. See Local Variables in Files, for basic information about file-local variables. This section describes the functions and variables that affect how file-local variables are processed.
If a file-local variable could specify an arbitrary function or Lisp expression that would be called later, visiting a file could take over your Emacs. Emacs protects against this by automatically setting only those file-local variables whose specified values are known to be safe. Other file-local variables are set only if the user agrees.
For additional safety, read-circle is temporarily bound to
nil when Emacs reads file-local variables (see Input Functions). This prevents the Lisp reader from recognizing circular
and shared Lisp structures (see 循环对象).
This variable controls whether to process file-local variables. The possible values are:
t(the default)- Set the safe variables, and query (once) about any unsafe variables.
:safe- Set only the safe variables and do not query.
:all- Set all the variables and do not query.
nil- Don't set any variables.
- anything else
- Query (once) about all the variables.
This function parses, and binds or evaluates as appropriate, any local variables specified by the contents of the current buffer. The variable
enable-local-variableshas its effect here. However, this function does not look for the ‘mode:’ local variable in the ‘-*-’ line.set-auto-modedoes that, also takingenable-local-variablesinto account (see Auto Major Mode).This function works by walking the alist stored in
file-local-variables-alistand applying each local variable in turn. It callsbefore-hack-local-variables-hookandhack-local-variables-hookbefore and after applying the variables, respectively.If the optional argument mode-only is non-
nil, then all this function does is returntif the ‘-*-’ line or the local variables list specifies a mode andnilotherwise. It does not set the mode nor any other file-local variable.
This buffer-local variable holds the alist of file-local variable settings. Each element of the alist is of the form
(var.value), where var is a symbol of the local variable and value is its value. When Emacs visits a file, it first collects all the file-local variables into this alist, and then thehack-local-variablesfunction applies them one by one.
Emacs calls this hook immediately before applying file-local variables stored in
file-local-variables-alist.
Emacs calls this hook immediately after it finishes applying file-local variables stored in
file-local-variables-alist.
You can specify safe values for a variable with a
safe-local-variable property. The property has to be a
function of one argument; any value is safe if the function returns
non-nil given that value. Many commonly-encountered file
variables have safe-local-variable properties; these include
fill-column, fill-prefix, and indent-tabs-mode.
For boolean-valued variables that are safe, use booleanp as the
property value. Lambda expressions should be quoted so that
describe-variable can display the predicate.
This variable provides another way to mark some variable values as safe. It is a list of cons cells
(var.val), where var is a variable name and val is a value which is safe for that variable.When Emacs asks the user whether or not to obey a set of file-local variable specifications, the user can choose to mark them as safe. Doing so adds those variable/value pairs to
safe-local-variable-values, and saves it to the user's custom file.
This function returns non-
nilif it is safe to give sym the value val, based on the above criteria.
Some variables are considered risky. A variable whose name
ends in any of ‘-command’, ‘-frame-alist’, ‘-function’,
‘-functions’, ‘-hook’, ‘-hooks’, ‘-form’,
‘-forms’, ‘-map’, ‘-map-alist’, ‘-mode-alist’,
‘-program’, or ‘-predicate’ is considered risky. The
variables ‘font-lock-keywords’, ‘font-lock-keywords’
followed by a digit, and ‘font-lock-syntactic-keywords’ are also
considered risky. Finally, any variable whose name has a
non-nil risky-local-variable property is considered
risky.
This function returns non-
nilif sym is a risky variable, based on the above criteria.
If a variable is risky, it will not be entered automatically into
safe-local-variable-values as described above. Therefore,
Emacs will always query before setting a risky variable, unless the
user explicitly allows the setting by customizing
safe-local-variable-values directly.
This variable holds a list of variables that should not be given local values by files. Any value specified for one of these variables is completely ignored.
The ‘Eval:’ “variable” is also a potential loophole, so Emacs normally asks for confirmation before handling it.
This variable controls processing of ‘Eval:’ in ‘-*-’ lines or local variables lists in files being visited. A value of
tmeans process them unconditionally;nilmeans ignore them; anything else means ask the user what to do for each file. The default value ismaybe.
This variable holds a list of expressions that are safe to evaluate when found in the ‘Eval:’ “variable” in a file local variables list.
If the expression is a function call and the function has a
safe-local-eval-function property, the property value
determines whether the expression is safe to evaluate. The property
value can be a predicate to call to test the expression, a list of
such predicates (it's safe if any predicate succeeds), or t
(always safe provided the arguments are constant).
Text properties are also potential loopholes, since their values could include functions to call. So Emacs discards all text properties from string values specified for file-local variables.
A directory can specify local variable values common to all files in that directory; Emacs uses these to create buffer-local bindings for those variables in buffers visiting any file in that directory. This is useful when the files in the directory belong to some project and therefore share the same local variables.
There are two different methods for specifying directory local variables: by putting them in a special file, or by defining a project class for that directory.
This constant is the name of the file where Emacs expects to find the directory-local variables. The name of the file is .dir-locals.el6. A file by that name in a directory causes Emacs to apply its settings to any file in that directory or any of its subdirectories. If some of the subdirectories have their own .dir-locals.el files, Emacs uses the settings from the deepest file it finds starting from the file's directory and moving up the directory tree. The file specifies local variables as a specially formatted list; see Per-directory Local Variables, for more details.
This function reads the
.dir-locals.elfile and stores the directory-local variables infile-local-variables-alistthat is local to the buffer visiting any file in the directory, without applying them. It also stores the directory-local settings indir-locals-class-alist, where it defines a special class for the directory in which .dir-locals.el file was found. This function works by callingdir-locals-set-class-variablesanddir-locals-set-directory-class, described below.
This function defines a set of variable settings for the named class, which is a symbol. You can later assign the class to one or more directories, and Emacs will apply those variable settings to all files in those directories. The list in variables can be of one of the two forms:
(major-mode.alist)or(directory.list). With the first form, if the file's buffer turns on a mode that is derived from major-mode, then the all the variables in the associated alist are applied; alist should be of the form(name.value). A special valuenilfor major-mode means the settings are applicable to any mode.With the second form of variables, if directory is the initial substring of the file's directory, then list is applied recursively by following the above rules; list should be of one of the two forms accepted by this function in variables.
This function assigns class to all the files in
directoryand its subdirectories. Thereafter, all the variable settings specified for class will be applied to any visited file in directory and its children. class must have been already defined bydir-locals-set-class-variables.Emacs uses this function internally when it loads directory variables from a
.dir-locals.elfile. In that case, the optional argument mtime holds the file modification time (as returned byfile-attributes). Emacs uses this time to check stored local variables are still valid. If you are assigning a class directly, not via a file, this argument should benil.
This alist holds the class symbols and the associated variable settings. It is updated by
dir-locals-set-class-variables.
This alist holds directory names, their assigned class names, and modification times of the associated directory local variables file (if there is one). The function
dir-locals-set-directory-classupdates this list.
In addition to buffer-local variable bindings (see Buffer-Local Variables), Emacs supports frame-local bindings. A frame-local binding for a variable is in effect in a frame for which it was defined.
In practice, frame-local variables have not proven very useful.
Ordinary frame parameters are generally used instead (see Frame Parameters). The function make-variable-frame-local, which
was used to define frame-local variables, has been deprecated since
Emacs 22.2. However, you can still define a frame-specific binding
for a variable var in frame frame, by setting the
var frame parameter for that frame:
(modify-frame-parameters frame '((var . value)))
This causes the variable var to be bound to the specified
value in the named frame. To check the frame-specific
values of such variables, use frame-parameter. See Parameter Access.
Note that you cannot have a frame-local binding for a variable that has a buffer-local binding.
It is sometimes useful to make two variables synonyms, so that both
variables always have the same value, and changing either one also
changes the other. Whenever you change the name of a
variable—either because you realize its old name was not well
chosen, or because its meaning has partly changed—it can be useful
to keep the old name as an alias of the new one for
compatibility. You can do this with defvaralias.
This function defines the symbol new-alias as a variable alias for symbol base-variable. This means that retrieving the value of new-alias returns the value of base-variable, and changing the value of new-alias changes the value of base-variable. The two aliased variable names always share the same value and the same bindings.
If the docstring argument is non-
nil, it specifies the documentation for new-alias; otherwise, the alias gets the same documentation as base-variable has, if any, unless base-variable is itself an alias, in which case new-alias gets the documentation of the variable at the end of the chain of aliases.This function returns base-variable.
Variable aliases are convenient for replacing an old name for a
variable with a new name. make-obsolete-variable declares that
the old name is obsolete and therefore that it may be removed at some
stage in the future.
This function makes the byte compiler warn that the variable obsolete-name is obsolete. If current-name is a symbol, it is the variable's new name; then the warning message says to use current-name instead of obsolete-name. If current-name is a string, this is the message and there is no replacement variable.
If provided, when should be a string indicating when the variable was first made obsolete—for example, a date or a release number.
You can make two variables synonyms and declare one obsolete at the
same time using the macro define-obsolete-variable-alias.
This macro marks the variable obsolete-name as obsolete and also makes it an alias for the variable current-name. It is equivalent to the following:
(defvaralias obsolete-name current-name docstring) (make-obsolete-variable obsolete-name current-name when)
This function returns the variable at the end of the chain of aliases of variable. If variable is not a symbol, or if variable is not defined as an alias, the function returns variable.
This function signals a
cyclic-variable-indirectionerror if there is a loop in the chain of symbols.
(defvaralias 'foo 'bar)
(indirect-variable 'foo)
⇒ bar
(indirect-variable 'bar)
⇒ bar
(setq bar 2)
bar
⇒ 2
foo
⇒ 2
(setq foo 0)
bar
⇒ 0
foo
⇒ 0
Ordinary Lisp variables can be assigned any value that is a valid
Lisp object. However, certain Lisp variables are not defined in Lisp,
but in C. Most of these variables are defined in the C code using
DEFVAR_LISP. Like variables defined in Lisp, these can take on
any value. However, some variables are defined using
DEFVAR_INT or DEFVAR_BOOL. See Writing Emacs Primitives, in particular the
description of functions of the type syms_of_filename,
for a brief discussion of the C implementation.
Variables of type DEFVAR_BOOL can only take on the values
nil or t. Attempting to assign them any other value
will set them to t:
(let ((display-hourglass 5))
display-hourglass)
⇒ t
Variables of type DEFVAR_INT can only take on integer values.
Attempting to assign them any other value will result in an error:
(setq window-min-height 5.0)
error--> Wrong type argument: integerp, 5.0
A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them.
In a general sense, a function is a rule for carrying on a computation given several values called arguments. The result of the computation is called the value of the function. The computation can also have side effects: lasting changes in the values of variables or the contents of data structures.
Here are important terms for functions in Emacs Lisp and for other function-like objects.
car or append. These functions are also called
built-in functions, or subrs. (Special forms are also
considered primitives.)
Usually the reason we implement a function as a primitive is either
because it is fundamental, because it provides a low-level interface
to operating system services, or because it needs to run fast.
Primitives can be modified or added only by changing the C sources and
recompiling the editor. See Writing Emacs Primitives.
command-execute can invoke; it
is a possible definition for a key sequence. Some functions are
commands; a function written in Lisp is a command if it contains an
interactive declaration (see Defining Commands). Such a function
can be called from Lisp expressions like other functions; in this case,
the fact that the function is a command makes no difference.
Keyboard macros (strings and vectors) are commands also, even though
they are not functions. A symbol is a command if its function
definition is a command; such symbols can be invoked with M-x.
The symbol is a function as well if the definition is a function.
See Interactive Call.
This function returns
tif object is any kind of function, i.e. can be passed tofuncall. Note thatfunctionpreturnsnilfor special forms (see Special Forms).
Unlike functionp, the next three functions do not
treat a symbol as its function definition.
This function returns
tif object is a built-in function (i.e., a Lisp primitive).(subrp 'message) ;messageis a symbol, ⇒ nil ; not a subr object. (subrp (symbol-function 'message)) ⇒ t
This function returns
tif object is a byte-code function. For example:(byte-code-function-p (symbol-function 'next-line)) ⇒ t
This function provides information about the argument list of a primitive, subr. The returned value is a pair
(min.max). min is the minimum number of args. max is the maximum number or the symbolmany, for a function with&restarguments, or the symbolunevalledif subr is a special form.
A function written in Lisp is a list that looks like this:
(lambda (arg-variables...)
[documentation-string]
[interactive-declaration]
body-forms...)
Such a list is called a lambda expression. In Emacs Lisp, it actually is valid as an expression—it evaluates to itself. In some other Lisp dialects, a lambda expression is not a valid expression at all. In either case, its main use is not to be evaluated as an expression, but to be called as a function.
A function written in Lisp (a “lambda expression”) is a list that looks like this:
(lambda (arg-variables...)
[documentation-string]
[interactive-declaration]
body-forms...)
The first element of a lambda expression is always the symbol
lambda. This indicates that the list represents a function. The
reason functions are defined to start with lambda is so that
other lists, intended for other uses, will not accidentally be valid as
functions.
The second element is a list of symbols—the argument variable names. This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See Local Variables.
The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See Function Documentation.
The interactive declaration is a list of the form (interactive
code-string). This declares how to provide arguments if the
function is used interactively. Functions with this declaration are called
commands; they can be called using M-x or bound to a key.
Functions not intended to be called in this way should not have interactive
declarations. See Defining Commands, for how to write an interactive
declaration.
The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, “a list of Lisp forms to evaluate”). The value returned by the function is the value returned by the last element of the body.
Consider for example the following function:
(lambda (a b c) (+ a b c))
We can call this function by writing it as the car of an expression, like this:
((lambda (a b c) (+ a b c))
1 2 3)
This call evaluates the body of the lambda expression with the variable
a bound to 1, b bound to 2, and c bound to 3.
Evaluation of the body adds these three numbers, producing the result 6;
therefore, this call to the function returns the value 6.
Note that the arguments can be the results of other function calls, as in this example:
((lambda (a b c) (+ a b c))
1 (* 2 3) (- 5 4))
This evaluates the arguments 1, (* 2 3), and (- 5
4) from left to right. Then it applies the lambda expression to the
argument values 1, 6 and 1 to produce the value 8.
It is not often useful to write a lambda expression as the car of
a form in this way. You can get the same result, of making local
variables and giving them values, using the special form let
(see Local Variables). And let is clearer and easier to use.
In practice, lambda expressions are either stored as the function
definitions of symbols, to produce named functions, or passed as
arguments to other functions (see Anonymous Functions).
However, calls to explicit lambda expressions were very useful in the
old days of Lisp, before the special form let was invented. At
that time, they were the only way to bind and initialize local
variables.
Our simple sample function, (lambda (a b c) (+ a b c)),
specifies three argument variables, so it must be called with three
arguments: if you try to call it with only two arguments or four
arguments, you get a wrong-number-of-arguments error.
It is often convenient to write a function that allows certain
arguments to be omitted. For example, the function substring
accepts three arguments—a string, the start index and the end
index—but the third argument defaults to the length of the
string if you omit it. It is also convenient for certain functions to
accept an indefinite number of arguments, as the functions list
and + do.
To specify optional arguments that may be omitted when a function
is called, simply include the keyword &optional before the optional
arguments. To specify a list of zero or more extra arguments, include the
keyword &rest before one final argument.
Thus, the complete syntax for an argument list is as follows:
(required-vars...
[&optional optional-vars...]
[&rest rest-var])
The square brackets indicate that the &optional and &rest
clauses, and the variables that follow them, are optional.
A call to the function requires one actual argument for each of the
required-vars. There may be actual arguments for zero or more of
the optional-vars, and there cannot be any actual arguments beyond
that unless the lambda list uses &rest. In that case, there may
be any number of extra actual arguments.
If actual arguments for the optional and rest variables are omitted,
then they always default to nil. There is no way for the
function to distinguish between an explicit argument of nil and
an omitted argument. However, the body of the function is free to
consider nil an abbreviation for some other meaningful value.
This is what substring does; nil as the third argument to
substring means to use the length of the string supplied.
Common Lisp note: Common Lisp allows the function to specify what
default value to use when an optional argument is omitted; Emacs Lisp
always uses nil. Emacs Lisp does not support “supplied-p”
variables that tell you whether an argument was explicitly passed.
For example, an argument list that looks like this:
(a b &optional c d &rest e)
binds a and b to the first two actual arguments, which are
required. If one or two more arguments are provided, c and
d are bound to them respectively; any arguments after the first
four are collected into a list and e is bound to that list. If
there are only two arguments, c is nil; if two or three
arguments, d is nil; if four arguments or fewer, e
is nil.
There is no way to have required arguments following optional
ones—it would not make sense. To see why this must be so, suppose
that c in the example were optional and d were required.
Suppose three actual arguments are given; which variable would the
third argument be for? Would it be used for the c, or for
d? One can argue for both possibilities. Similarly, it makes
no sense to have any more arguments (either required or optional)
after a &rest argument.
Here are some examples of argument lists and proper calls:
((lambda (n) (1+ n)) ; One required: 1) ; requires exactly one argument. ⇒ 2 ((lambda (n &optional n1) ; One required and one optional: (if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments. 1 2) ⇒ 3 ((lambda (n &rest ns) ; One required and one rest: (+ n (apply '+ ns))) ; 1 or more arguments. 1 2 3 4 5) ⇒ 15
A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See Documentation, for how the documentation-string is accessed.
It is a good idea to provide documentation strings for all the functions in your program, even those that are called only from within your program. Documentation strings are like comments, except that they are easier to access.
The first line of the documentation string should stand on its own,
because apropos displays just this first line. It should consist
of one or two complete sentences that summarize the function's purpose.
The start of the documentation string is usually indented in the source file, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up in the program source. That is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands.
You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation.
The last line of the documentation string can specify calling conventions different from the actual function arguments. Write text like this:
\(fn arglist)
following a blank line, at the beginning of the line, with no newline following it inside the documentation string. (The ‘\’ is used to avoid confusing the Emacs motion commands.) The calling convention specified in this way appears in help messages in place of the one derived from the actual arguments of the function.
This feature is particularly useful for macro definitions, since the arguments written in a macro definition often do not correspond to the way users think of the parts of the macro call.
In most computer languages, every function has a name; the idea of a
function without a name is nonsensical. In Lisp, a function in the
strictest sense has no name. It is simply a list whose first element is
lambda, a byte-code function object, or a primitive subr-object.
However, a symbol can serve as the name of a function. This happens when you put the function in the symbol's function cell (see Symbol Components). Then the symbol itself becomes a valid, callable function, equivalent to the list or subr-object that its function cell refers to. The contents of the function cell are also called the symbol's function definition. The procedure of using a symbol's function definition in place of the symbol is called symbol function indirection; see Function Indirection.
In practice, nearly all functions are given names in this way and
referred to through their names. For example, the symbol car works
as a function and does what it does because the primitive subr-object
#<subr car> is stored in its function cell.
We give functions names because it is convenient to refer to them by
their names in Lisp expressions. For primitive subr-objects such as
#<subr car>, names are the only way you can refer to them: there
is no read syntax for such objects. For functions written in Lisp, the
name is more convenient to use in a call than an explicit lambda
expression. Also, a function with a name can refer to itself—it can
be recursive. Writing the function's name in its own definition is much
more convenient than making the function definition point to itself
(something that is not impossible but that has various disadvantages in
practice).
We often identify functions with the symbols used to name them. For
example, we often speak of “the function car,” not
distinguishing between the symbol car and the primitive
subr-object that is its function definition. For most purposes, the
distinction is not important.
Even so, keep in mind that a function need not have a unique name. While
a given function object usually appears in the function cell of only
one symbol, this is just a matter of convenience. It is easy to store
it in several symbols using fset; then each of the symbols is
equally well a name for the same function.
A symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict. (Some Lisp dialects, such as Scheme, do not distinguish between a symbol's value and its function definition; a symbol's value as a variable is also its function definition.) If you have not given a symbol a function definition, you cannot use it as a function; whether the symbol has a value as a variable makes no difference to this.
We usually give a name to a function when it is first created. This
is called defining a function, and it is done with the
defun special form.
defunis the usual way to define new Lisp functions. It defines the symbol name as a function that looks like this:(lambda argument-list . body-forms)
defunstores this lambda expression in the function cell of name. It returns the value name, but usually we ignore this value.As described previously, argument-list is a list of argument names and may include the keywords
&optionaland&rest(see Lambda Expressions). Also, the first two of the body-forms may be a documentation string and an interactive declaration.There is no conflict if the same symbol name is also used as a variable, since the symbol's value cell is independent of the function cell. See Symbol Components.
Here are some examples:
(defun foo () 5) ⇒ foo (foo) ⇒ 5 (defun bar (a &optional b &rest c) (list a b c)) ⇒ bar (bar 1 2 3 4 5) ⇒ (1 2 (3 4 5)) (bar 1) ⇒ (1 nil nil) (bar) error--> Wrong number of arguments. (defun capitalize-backwards () "Upcase the last letter of a word." (interactive) (backward-word 1) (forward-word 1) (backward-char 1) (capitalize-word 1)) ⇒ capitalize-backwardsBe careful not to redefine existing functions unintentionally.
defunredefines even primitive functions such ascarwithout any hesitation or notification. Redefining a function already defined is often done deliberately, and there is no way to distinguish deliberate redefinition from unintentional redefinition.
This special form defines the symbol name as a function, with definition definition (which can be any valid Lisp function). It returns definition.
If docstring is non-
nil, it becomes the function documentation of name. Otherwise, any documentation provided by definition is used.The proper place to use
defaliasis where a specific function name is being defined—especially where that name appears explicitly in the source file being loaded. This is becausedefaliasrecords which file defined the function, just likedefun(see Unloading).By contrast, in programs that manipulate function definitions for other purposes, it is better to use
fset, which does not keep such records. See Function Cells.
You cannot create a new primitive function with defun or
defalias, but you can use them to change the function definition of
any symbol, even one such as car or x-popup-menu whose
normal definition is a primitive. However, this is risky: for
instance, it is next to impossible to redefine car without
breaking Lisp completely. Redefining an obscure function such as
x-popup-menu is less dangerous, but it still may not work as
you expect. If there are calls to the primitive from C code, they
call the primitive's C definition directly, so changing the symbol's
definition will have no effect on them.
See also defsubst, which defines a function like defun
and tells the Lisp compiler to open-code it. See Inline Functions.
Defining functions is only half the battle. Functions don't do anything until you call them, i.e., tell them to run. Calling a function is also known as invocation.
The most common way of invoking a function is by evaluating a list.
For example, evaluating the list (concat "a" "b") calls the
function concat with arguments "a" and "b".
See Evaluation, for a description of evaluation.
When you write a list as an expression in your program, you specify
which function to call, and how many arguments to give it, in the text
of the program. Usually that's just what you want. Occasionally you
need to compute at run time which function to call. To do that, use
the function funcall. When you also need to determine at run
time how many arguments to pass, use apply.
funcallcalls function with arguments, and returns whatever function returns.Since
funcallis a function, all of its arguments, including function, are evaluated beforefuncallis called. This means that you can use any expression to obtain the function to be called. It also means thatfuncalldoes not see the expressions you write for the arguments, only their values. These values are not evaluated a second time in the act of calling function; the operation offuncallis like the normal procedure for calling a function, once its arguments have already been evaluated.The argument function must be either a Lisp function or a primitive function. Special forms and macros are not allowed, because they make sense only when given the “unevaluated” argument expressions.
funcallcannot provide these because, as we saw above, it never knows them in the first place.(setq f 'list) ⇒ list (funcall f 'x 'y 'z) ⇒ (x y z) (funcall f 'x 'y '(z)) ⇒ (x y (z)) (funcall 'and t nil) error--> Invalid function: #<subr and>Compare these examples with the examples of
apply.
applycalls function with arguments, just likefuncallbut with one difference: the last of arguments is a list of objects, which are passed to function as separate arguments, rather than a single list. We say thatapplyspreads this list so that each individual element becomes an argument.
applyreturns the result of calling function. As withfuncall, function must either be a Lisp function or a primitive function; special forms and macros do not make sense inapply.(setq f 'list) ⇒ list (apply f 'x 'y 'z) error--> Wrong type argument: listp, z (apply '+ 1 2 '(3 4)) ⇒ 10 (apply '+ '(1 2 3 4)) ⇒ 10 (apply 'append '((a b c) nil (x y z) nil)) ⇒ (a b c x y z)For an interesting example of using
apply, see Definition of mapcar.
Sometimes it is useful to fix some of the function's arguments at certain values, and leave the rest of arguments for when the function is actually called. The act of fixing some of the function's arguments is called partial application of the function7. The result is a new function that accepts the rest of arguments and calls the original function with all the arguments combined.
Here's how to do partial application in Emacs Lisp:
This function returns a new function which, when called, will call func with the list of arguments composed from args and additional arguments specified at the time of the call. If func accepts n arguments, then a call to
apply-partiallywith m<n arguments will produce a new function of n-m arguments.Here's how we could define the built-in function
1+, if it didn't exist, usingapply-partiallyand+, another built-in function:(defalias '1+ (apply-partially '+ 1) "Increment argument by one.") (1+ 10) ⇒ 11
It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using funcall or apply. Functions
that accept function arguments are often called functionals.
Sometimes, when you call a functional, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function:
A mapping function applies a given function (not a
special form or macro) to each element of a list or other collection.
Emacs Lisp has several such functions; mapcar and
mapconcat, which scan a list, are described here.
See Definition of mapatoms, for the function mapatoms which
maps over the symbols in an obarray. See Definition of maphash,
for the function maphash which maps over key/value associations
in a hash table.
These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large. To map
over a char-table in a way that deals properly with its sparse nature,
use the function map-char-table (see Char-Tables).
mapcarapplies function to each element of sequence in turn, and returns a list of the results.The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. The result is always a list. The length of the result is the same as the length of sequence. For example:
(mapcar 'car '((a b) (c d) (e f))) ⇒ (a c e) (mapcar '1+ [1 2 3]) ⇒ (2 3 4) (mapcar 'string "abc") ⇒ ("a" "b" "c") ;; Call each function inmy-hooks. (mapcar 'funcall my-hooks) (defun mapcar* (function &rest args) "Apply FUNCTION to successive cars of all ARGS. Return the list of results." ;; If no list is exhausted, (if (not (memq nil args)) ;; apply function to cars. (cons (apply function (mapcar 'car args)) (apply 'mapcar* function ;; Recurse for rest of elements. (mapcar 'cdr args))))) (mapcar* 'cons '(a b c) '(1 2 3 4)) ⇒ ((a . 1) (b . 2) (c . 3))
mapcis likemapcarexcept that function is used for side-effects only—the values it returns are ignored, not collected into a list.mapcalways returns sequence.
mapconcatapplies function to each element of sequence: the results, which must be strings, are concatenated. Between each pair of result strings,mapconcatinserts the string separator. Usually separator contains a space or comma or other suitable punctuation.The argument function must be a function that can take one argument and return a string. The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string.
(mapconcat 'symbol-name '(The cat in the hat) " ") ⇒ "The cat in the hat" (mapconcat (function (lambda (x) (format "%c" (1+ x)))) "HAL-8000" "") ⇒ "IBM.9111"
In Lisp, a function is a list that starts with lambda, a
byte-code function compiled from such a list, or alternatively a
primitive subr-object; names are “extra.” Although functions are
usually defined with defun and given names at the same time, it
is occasionally more concise to use an explicit lambda expression—an
anonymous function. Such a list is valid wherever a function name is.
Any method of creating such a list makes a valid function. Even this:
(setq silly (append '(lambda (x)) (list (list '+ (* 3 4) 'x))))
⇒ (lambda (x) (+ 12 x))
This computes a list that looks like (lambda (x) (+ 12 x)) and
makes it the value (not the function definition!) of
silly.
Here is how we might call this function:
(funcall silly 1)
⇒ 13
It does not work to write (silly 1), because this
function is not the function definition of silly. We
have not given silly any function definition, just a value as a
variable.
Most of the time, anonymous functions are constants that appear in
your program. For instance, you might want to pass one as an argument
to the function mapcar, which applies any given function to
each element of a list (see Mapping Functions).
See describe-symbols example, for a realistic example of this.
In the following example, we define a change-property
function that takes a function as its third argument, followed by a
double-property function that makes use of
change-property by passing it an anonymous function:
(defun change-property (symbol prop function)
(let ((value (get symbol prop)))
(put symbol prop (funcall function value))))
(defun double-property (symbol prop)
(change-property symbol prop (lambda (x) (* 2 x))))
In the double-property function, we did not quote the
lambda form. This is permissible, because a lambda form
is self-quoting: evaluating the form yields the form itself.
Whether or not you quote a lambda form makes a difference if
you compile the code (see Byte Compilation). If the lambda
form is unquoted, as in the above example, the anonymous function is
also compiled. Suppose, however, that we quoted the lambda
form:
(defun double-property (symbol prop)
(change-property symbol prop '(lambda (x) (* 2 x))))
If you compile this, the argument passed to change-property is
the precise list shown:
(lambda (x) (* x 2))
The Lisp compiler cannot assume this list is a function, even though
it looks like one, since it does not know what change-property
will do with the list. Perhaps it will check whether the car of
the third element is the symbol *!
The function special form explicitly tells the byte-compiler
that its argument is a function:
This special form returns function-object without evaluating it. In this, it is equivalent to
quote. However, it serves as a note to the Emacs Lisp compiler that function-object is intended to be used only as a function, and therefore can safely be compiled. Contrast this withquote, in Quoting.
The read syntax #' is a short-hand for using function.
Generally, it is not necessary to use either #' or
function; just use an unquoted lambda form instead.
(Actually, lambda is a macro defined using function.)
The following forms are all equivalent:
#'(lambda (x) (* x x))
(function (lambda (x) (* x x)))
(lambda (x) (* x x))
We sometimes write function instead of quote when
quoting the name of a function, but this usage is just a sort of
comment:
(function symbol) == (quote symbol) == 'symbol
The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.
See also the function indirect-function. See Definition of indirect-function.
This returns the object in the function cell of symbol. If the symbol's function cell is void, a
void-functionerror is signaled.This function does not check that the returned object is a legitimate function.
(defun bar (n) (+ n 2)) ⇒ bar (symbol-function 'bar) ⇒ (lambda (n) (+ n 2)) (fset 'baz 'bar) ⇒ bar (symbol-function 'baz) ⇒ bar
If you have never given a symbol any function definition, we say that
that symbol's function cell is void. In other words, the function
cell does not have any Lisp object in it. If you try to call such a symbol
as a function, it signals a void-function error.
Note that void is not the same as nil or the symbol
void. The symbols nil and void are Lisp objects,
and can be stored into a function cell just as any other object can be
(and they can be valid functions if you define them in turn with
defun). A void function cell contains no object whatsoever.
You can test the voidness of a symbol's function definition with
fboundp. After you have given a symbol a function definition, you
can make it void once more using fmakunbound.
This function returns
tif the symbol has an object in its function cell,nilotherwise. It does not check that the object is a legitimate function.
This function makes symbol's function cell void, so that a subsequent attempt to access this cell will cause a
void-functionerror. It returns symbol. (See alsomakunbound, in Void Variables.)(defun foo (x) x) ⇒ foo (foo 1) ⇒1 (fmakunbound 'foo) ⇒ foo (foo 1) error--> Symbol's function definition is void: foo
This function stores definition in the function cell of symbol. The result is definition. Normally definition should be a function or the name of a function, but this is not checked. The argument symbol is an ordinary evaluated argument.
There are three normal uses of this function:
- Copying one symbol's function definition to another—in other words, making an alternate name for a function. (If you think of this as the definition of the new name, you should use
defaliasinstead offset; see Definition of defalias.)- Giving a symbol a function definition that is not a list and therefore cannot be made with
defun. For example, you can usefsetto give a symbols1a function definition which is another symbols2; thens1serves as an alias for whatever definitions2presently has. (Once again usedefaliasinstead offsetif you think of this as the definition ofs1.)- In constructs for defining or altering functions. If
defunwere not a primitive, it could be written in Lisp (as a macro) usingfset.Here are examples of these uses:
;; Savefoo's definition inold-foo. (fset 'old-foo (symbol-function 'foo)) ;; Make the symbolcarthe function definition ofxfirst. ;; (Most likely,defaliaswould be better thanfsethere.) (fset 'xfirst 'car) ⇒ car (xfirst '(1 2 3)) ⇒ 1 (symbol-function 'xfirst) ⇒ car (symbol-function (symbol-function 'xfirst)) ⇒ #<subr car> ;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") ⇒ "\^u2\^k" ;; Here is a function that alters other functions. (defun copy-function-definition (new old) "Define NEW with the same function definition as OLD." (fset new (symbol-function old)))
fset is sometimes used to save the old definition of a
function before redefining it. That permits the new definition to
invoke the old definition. But it is unmodular and unclean for a Lisp
file to redefine a function defined elsewhere. If you want to modify
a function defined by another package, it is cleaner to use
defadvice (see Advising Functions).
You can use make-obsolete to declare a function obsolete. This
indicates that the function may be removed at some stage in the future.
This function makes the byte compiler warn that the function obsolete-name is obsolete. If current-name is a symbol, the warning message says to use current-name instead of obsolete-name. current-name does not need to be an alias for obsolete-name; it can be a different function with similar functionality. If current-name is a string, it is the warning message.
If provided, when should be a string indicating when the function was first made obsolete—for example, a date or a release number.
You can define a function as an alias and declare it obsolete at the
same time using the macro define-obsolete-function-alias:
This macro marks the function obsolete-name obsolete and also defines it as an alias for the function current-name. It is equivalent to the following:
(defalias obsolete-name current-name docstring) (make-obsolete obsolete-name current-name when)
In addition, you can mark a certain a particular calling convention for a function as obsolete:
This function specifies the argument list signature as the correct way to call function. This causes the Emacs byte compiler to issue a warning whenever it comes across an Emacs Lisp program that calls function any other way (however, it will still allow the code to be byte compiled).
For instance, in old versions of Emacs the
sit-forfunction accepted three arguments, like this(sit-for seconds milliseconds nodisp)However, calling
sit-forthis way is considered obsolete (see Waiting). The old calling convention is deprecated like this:(set-advertised-calling-convention 'sit-for '(seconds &optional nodisp))
You can define an inline function by using defsubst instead
of defun. An inline function works just like an ordinary
function except for one thing: when you compile a call to the function,
the function's definition is open-coded into the caller.
Making a function inline makes explicit calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them.
Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline.
Also, inline functions do not behave well with respect to debugging,
tracing, and advising (see Advising Functions). Since ease of
debugging and the flexibility of redefining functions are important
features of Emacs, you should not make a function inline, even if it's
small, unless its speed is really crucial, and you've timed the code
to verify that using defun actually has performance problems.
It's possible to define a macro to expand into the same code that an
inline function would execute. (See Macros.) But the macro would be
limited to direct use in expressions—a macro cannot be called with
apply, mapcar and so on. Also, it takes some work to
convert an ordinary function into a macro. To convert it into an inline
function is very easy; simply replace defun with defsubst.
Since each argument of an inline function is evaluated exactly once, you
needn't worry about how many times the body uses the arguments, as you
do for macros. (See Argument Evaluation.)
Inline functions can be used and open-coded later on in the same file, following the definition, just like macros.
Byte-compiling a file often produces warnings about functions that the compiler doesn't know about (see Compiler Errors). Sometimes this indicates a real problem, but usually the functions in question are defined in other files which would be loaded if that code is run. For example, byte-compiling fortran.el used to warn:
In end of data:
fortran.el:2152:1:Warning: the function `gud-find-c-expr' is not known
to be defined.
In fact, gud-find-c-expr is only used in the function that
Fortran mode uses for the local value of
gud-find-expr-function, which is a callback from GUD; if it is
called, the GUD functions will be loaded. When you know that such a
warning does not indicate a real problem, it is good to suppress the
warning. That makes new warnings which might mean real problems more
visible. You do that with declare-function.
All you need to do is add a declare-function statement before the
first use of the function in question:
(declare-function gud-find-c-expr "gud.el" nil)
This says that gud-find-c-expr is defined in gud.el (the
‘.el’ can be omitted). The compiler takes for granted that that file
really defines the function, and does not check.
The optional third argument specifies the argument list of
gud-find-c-expr. In this case, it takes no arguments
(nil is different from not specifying a value). In other
cases, this might be something like (file &optional overwrite).
You don't have to specify the argument list, but if you do the
byte compiler can check that the calls match the declaration.
Tell the byte compiler to assume that function is defined, with arguments arglist, and that the definition should come from the file file. fileonly non-
nilmeans only check that file exists, not that it actually defines function.
To verify that these functions really are declared where
declare-function says they are, use check-declare-file
to check all declare-function calls in one source file, or use
check-declare-directory check all the files in and under a
certain directory.
These commands find the file that ought to contain a function's
definition using locate-library; if that finds no file, they
expand the definition file name relative to the directory of the file
that contains the declare-function call.
You can also say that a function is defined by C code by specifying a
file name ending in ‘.c’ or ‘.m’. check-declare-file
looks for these files in the C source code directory. This is useful
only when you call a function that is defined only on certain systems.
Most of the primitive functions of Emacs are always defined so they will
never give you a warning.
Sometimes a file will optionally use functions from an external package.
If you prefix the filename in the declare-function statement with
‘ext:’, then it will be checked if it is found, otherwise skipped
without error.
There are some function definitions that ‘check-declare’ does not
understand (e.g. defstruct and some other macros). In such cases,
you can pass a non-nil fileonly argument to
declare-function, meaning to only check that the file exists, not
that it actually defines the function. Note that to do this without
having to specify an argument list, you should set the arglist
argument to t (because nil means an empty argument list, as
opposed to an unspecified one).
Some major modes such as SES call functions that are stored in user files. (see Top, for more information on SES.) User files sometimes have poor pedigrees—you can get a spreadsheet from someone you've just met, or you can get one through email from someone you've never met. So it is risky to call a function whose source code is stored in a user file until you have determined that it is safe.
Returns
nilif form is a safe Lisp expression, or returns a list that describes why it might be unsafe. The argument unsafep-vars is a list of symbols known to have temporary bindings at this point; it is mainly used for internal recursive calls. The current buffer is an implicit argument, which provides a list of buffer-local bindings.
Being quick and simple, unsafep does a very light analysis and
rejects many Lisp expressions that are actually safe. There are no
known cases where unsafep returns nil for an unsafe
expression. However, a “safe” Lisp expression can return a string
with a display property, containing an associated Lisp
expression to be executed after the string is inserted into a buffer.
This associated expression can be a virus. In order to be safe, you
must delete properties from all strings calculated by user code before
inserting them into buffers.
Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here.
applyautoloadcall-interactivelycalled-interactively-pcommandpdocumentationevalfuncallfunctionignoreindirect-functioninteractiveinteractive-pmapatomsmapcarmap-char-tablemapconcatundefinedMacros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro.
Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them.
If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See Inline Functions.
Suppose we would like to define a Lisp construct to increment a
variable value, much like the ++ operator in C. We would like to
write (inc x) and have the effect of (setq x (1+ x)).
Here's a macro definition that does the job:
(defmacro inc (var)
(list 'setq var (list '1+ var)))
When this is called with (inc x), the argument var is the
symbol x—not the value of x, as it would
be in a function. The body of the macro uses this to construct the
expansion, which is (setq x (1+ x)). Once the macro definition
returns this expansion, Lisp proceeds to evaluate it, thus incrementing
x.
A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list.
Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked. The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a &rest argument. And the macro body executes and
returns its value just as a function body does.
The second crucial difference between macros and functions is that the value returned by the macro body is not the value of the macro call. Instead, it is an alternate expression for computing that value, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro.
Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual.
You can see the expansion of a given macro call by calling
macroexpand.
This function expands form, if it is a macro call. If the result is another macro call, it is expanded in turn, until something which is not a macro call results. That is the value returned by
macroexpand. If form is not a macro call to begin with, it is returned as given.Note that
macroexpanddoes not look at the subexpressions of form (although some macro definitions may do so). Even if they are macro calls themselves,macroexpanddoes not expand them.The function
macroexpanddoes not expand calls to inline functions. Normally there is no need for that, since a call to an inline function is no harder to understand than a call to an ordinary function.If environment is provided, it specifies an alist of macro definitions that shadow the currently defined macros. Byte compilation uses this feature.
(defmacro inc (var) (list 'setq var (list '1+ var))) ⇒ inc (macroexpand '(inc r)) ⇒ (setq r (1+ r)) (defmacro inc2 (var1 var2) (list 'progn (list 'inc var1) (list 'inc var2))) ⇒ inc2 (macroexpand '(inc2 r s)) ⇒ (progn (inc r) (inc s)) ;incnot expanded here.
macroexpand-allexpands macros likemacroexpand, but will look for and expand all macros in form, not just at the top-level. If no macros are expanded, the return value iseqto form.Repeating the example used for
macroexpandabove withmacroexpand-all, we see thatmacroexpand-alldoes expand the embedded calls toinc:(macroexpand-all '(inc2 r s)) ⇒ (progn (setq r (1+ r)) (setq s (1+ s)))
You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation.
When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself—they would be computed at compile time, which is not useful.
In order for compilation of macro calls to work, the macros must
already be defined in Lisp when the calls to them are compiled. The
compiler has a special feature to help you do this: if a file being
compiled contains a defmacro form, the macro is defined
temporarily for the rest of the compilation of that file.
Byte-compiling a file also executes any require calls at
top-level in the file, so you can ensure that necessary macro
definitions are available during compilation by requiring the files
that define them (see Named Features). To avoid loading the macro
definition files when someone runs the compiled program, write
eval-when-compile around the require calls (see Eval During Compile).
A Lisp macro is a list whose car is macro. Its cdr should
be a function; expansion of the macro works by applying the function
(with apply) to the list of unevaluated argument-expressions
from the macro call.
It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to pass
an anonymous macro to functionals such as mapcar. In practice,
all Lisp macros have names, and they are usually defined with the
special form defmacro.
defmacrodefines the symbol name as a macro that looks like this:(macro lambda argument-list . body-forms)(Note that the cdr of this list is a function—a lambda expression.) This macro object is stored in the function cell of name. The value returned by evaluating the
defmacroform is name, but usually we ignore this value.The shape and meaning of argument-list is the same as in a function, and the keywords
&restand&optionalmay be used (see Argument List). Macros may have a documentation string, but anyinteractivedeclaration is ignored since macros cannot be called interactively.
The body of the macro definition can include a declare form,
which can specify how <TAB> should indent macro calls, and how to
step through them for Edebug.
A
declareform is used in a macro definition to specify various additional information about it. Two kinds of specification are currently supported:
(debugedebug-form-spec)- Specify how to step through macro calls for Edebug. See Instrumenting Macro Calls.
(indentindent-spec)- Specify how to indent calls to this macro. See Indenting Macros, for more details.
A
declareform only has its special effect in the body of adefmacroform if it immediately follows the documentation string, if present, or the argument list otherwise. (Strictly speaking, severaldeclareforms can follow the documentation string or argument list, but since adeclareform can have several specs, they can always be combined into a single form.) When used at other places in adefmacroform, or outside adefmacroform,declarejust returnsnilwithout evaluating any specs.
No macro absolutely needs a declare form, because that form
has no effect on how the macro expands, on what the macro means in the
program. It only affects secondary features: indentation and Edebug.
Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the ‘`’ syntax (usually called backquote).
Backquote allows you to quote a list, but selectively evaluate
elements of that list. In the simplest case, it is identical to the
special form quote (see Quoting). For example, these
two forms yield identical results:
`(a list of (+ 2 3) elements)
⇒ (a list of (+ 2 3) elements)
'(a list of (+ 2 3) elements)
⇒ (a list of (+ 2 3) elements)
The special marker ‘,’ inside of the argument to backquote indicates a value that isn't constant. Backquote evaluates the argument of ‘,’ and puts the value in the list structure:
(list 'a 'list 'of (+ 2 3) 'elements)
⇒ (a list of 5 elements)
`(a list of ,(+ 2 3) elements)
⇒ (a list of 5 elements)
Substitution with ‘,’ is allowed at deeper levels of the list structure also. For example:
(defmacro t-becomes-nil (variable)
`(if (eq ,variable t)
(setq ,variable nil)))
(t-becomes-nil foo)
== (if (eq foo t) (setq foo nil))
You can also splice an evaluated value into the resulting list, using the special marker ‘,@’. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ‘`’ is often unreadable. Here are some examples:
(setq some-list '(2 3))
⇒ (2 3)
(cons 1 (append some-list '(4) some-list))
⇒ (1 2 3 4 2 3)
`(1 ,@some-list 4 ,@some-list)
⇒ (1 2 3 4 2 3)
(setq list '(hack foo bar))
⇒ (hack foo bar)
(cons 'use
(cons 'the
(cons 'words (append (cdr list) '(as elements)))))
⇒ (use the words foo bar as elements)
`(use the words ,@(cdr list) as elements)
⇒ (use the words foo bar as elements)
The basic facts of macro expansion have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.
The most common problem in writing macros is doing some of the real work prematurely—while expanding the macro, rather than in the expansion itself. For instance, one real package had this macro definition:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
(set-buffer-multibyte arg)))
With this erroneous macro definition, the program worked fine when
interpreted but failed when compiled. This macro definition called
set-buffer-multibyte during compilation, which was wrong, and
then did nothing when the compiled package was run. The definition
that the programmer really wanted was this:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
`(set-buffer-multibyte ,arg)))
This macro expands, if appropriate, into a call to
set-buffer-multibyte that will be executed when the compiled
program is actually run.
When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a simple “for” loop such as one might find in Pascal.
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(list 'let (list (list var init))
(cons 'while (cons (list '<= var final)
(append body (list (list 'inc var)))))))
⇒ for
(for i from 1 to 3 do
(setq square (* i i))
(princ (format "\n%d %d" i square)))
==>
(let ((i 1))
(while (<= i 3)
(setq square (* i i))
(princ (format "\n%d %d" i square))
(inc i)))
-|1 1
-|2 4
-|3 9
⇒ nil
The arguments from, to, and do in this macro are
“syntactic sugar”; they are entirely ignored. The idea is that you
will write noise words (such as from, to, and do)
in those positions in the macro call.
Here's an equivalent definition simplified through use of backquote:
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
`(let ((,var ,init))
(while (<= ,var ,final)
,@body
(inc ,var))))
Both forms of this definition (with backquote and without) suffer from
the defect that final is evaluated on every iteration. If
final is a constant, this is not a problem. If it is a more
complex form, say (long-complex-calculation x), this can slow
down the execution significantly. If final has side effects,
executing it more than once is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the for macro:
(let ((i 1)
(max 3))
(while (<= i max)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
Here is a macro definition that creates this expansion:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
Unfortunately, this fix introduces another problem, described in the following section.
In the previous section, the definition of for was fixed as
follows to make the expansion evaluate the macro arguments the proper
number of times:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
The new definition of for has a new problem: it introduces a
local variable named max which the user does not expect. This
causes trouble in examples such as the following:
(let ((max 0))
(for x from 0 to 10 do
(let ((this (frob x)))
(if (< max this)
(setq max this)))))
The references to max inside the body of the for, which
are supposed to refer to the user's binding of max, really access
the binding made by for.
The way to correct this is to use an uninterned symbol instead of
max (see Creating Symbols). The uninterned symbol can be
bound and referred to just like any other symbol, but since it is
created by for, we know that it cannot already appear in the
user's program. Since it is not interned, there is no way the user can
put it into the program later. It will never appear anywhere except
where put by for. Here is a definition of for that works
this way:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(let ((tempvar (make-symbol "max")))
`(let ((,var ,init)
(,tempvar ,final))
(while (<= ,var ,tempvar)
,@body
(inc ,var)))))
This creates an uninterned symbol named max and puts it in the
expansion instead of the usual interned symbol max that appears
in expressions ordinarily.
Another problem can happen if the macro definition itself
evaluates any of the macro argument expressions, such as by calling
eval (see Eval). If the argument is supposed to refer to the
user's variables, you may have trouble if the user happens to use a
variable with the same name as one of the macro arguments. Inside the
macro body, the macro argument binding is the most local binding of this
variable, so any references inside the form being evaluated do refer to
it. Here is an example:
(defmacro foo (a)
(list 'setq (eval a) t))
⇒ foo
(setq x 'b)
(foo x) ==> (setq b t)
⇒ t ; and b has been set.
;; but
(setq a 'c)
(foo a) ==> (setq a t)
⇒ t ; but this set a, not c.
It makes a difference whether the user's variable is named a or
x, because a conflicts with the macro argument variable
a.
Another problem with calling eval in a macro definition is that
it probably won't do what you intend in a compiled program. The
byte compiler runs macro definitions while compiling the program, when
the program's own computations (which you might have wished to access
with eval) don't occur and its local variable bindings don't
exist.
To avoid these problems, don't evaluate an argument expression while computing the macro expansion. Instead, substitute the expression into the macro expansion, so that its value will be computed as part of executing the expansion. This is how the other examples in this chapter work.
Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded.
Therefore, you should avoid side effects in computation of the macro expansion, unless you really know what you are doing.
One special kind of side effect can't be avoided: constructing Lisp objects. Almost all macro expansions include constructed lists; that is the whole point of most macros. This is usually safe; there is just one case where you must be careful: when the object you construct is part of a quoted constant in the macro expansion.
If the macro is expanded just once, in compilation, then the object is constructed just once, during compilation. But in interpreted execution, the macro is expanded each time the macro call runs, and this means a new object is constructed each time.
In most clean Lisp code, this difference won't matter. It can matter only if you perform side-effects on the objects constructed by the macro definition. Thus, to avoid trouble, avoid side effects on objects constructed by macro definitions. Here is an example of how such side effects can get you into trouble:
(defmacro empty-object ()
(list 'quote (cons nil nil)))
(defun initialize (condition)
(let ((object (empty-object)))
(if condition
(setcar object condition))
object))
If initialize is interpreted, a new list (nil) is
constructed each time initialize is called. Thus, no side effect
survives between calls. If initialize is compiled, then the
macro empty-object is expanded during compilation, producing a
single “constant” (nil) that is reused and altered each time
initialize is called.
One way to avoid pathological cases like this is to think of
empty-object as a funny kind of constant, not as a memory
allocation construct. You wouldn't use setcar on a constant such
as '(nil), so naturally you won't use it on (empty-object)
either.
You can use the declare form in the macro definition to
specify how to <TAB> should indent calls to the macro. You
write it like this:
(declare (indent indent-spec))
Here are the possibilities for indent-spec:
nildefunlisp-body-indent
more columns than the open-parenthesis starting the containing
expression. If the argument is distinguished and is either the first
or second argument, it is indented twice that many extra columns.
If the argument is distinguished and not the first or second argument,
the line uses the standard pattern.
parse-partial-sexp (a Lisp primitive for
indentation and nesting computation) when it parses up to the
beginning of this line.
This chapter describes how to declare user options for customization, and also customization groups for classifying them. We use the term customization item to include both kinds of customization definitions—as well as face definitions (see Defining Faces).
All kinds of customization declarations (for variables and groups, and for faces) accept keyword arguments for specifying various information. This section describes some keywords that apply to all kinds.
All of these keywords, except :tag, can be used more than once
in a given item. Each use of the keyword has an independent effect.
The keyword :tag is an exception because any given item can only
display one name.
:tag label:group group:group in a defgroup, it makes the new group a subgroup of
group.
If you use this keyword more than once, you can put a single item into
more than one group. Displaying any of those groups will show this
item. Please don't overdo this, since the result would be annoying.
:link link-dataThere are several alternatives you can use for link-data:
(custom-manual info-node)"(emacs)Top". The link appears as
‘[Manual]’ in the customization buffer and enters the built-in
Info reader on info-node.
(info-link info-node)custom-manual except that the link appears
in the customization buffer with the Info node name.
(url-link url)browse-url-browser-function.
(emacs-commentary-link library)(emacs-library-link library)(file-link file)find-file when the user invokes this link.
(function-link function)describe-function when the user invokes this link.
(variable-link variable)describe-variable when the user invokes this link.
(custom-group-link group)You can specify the text to use in the customization buffer by adding
:tag name after the first element of the link-data;
for example, (info-link :tag "foo" "(emacs)Top") makes a link to
the Emacs manual which appears in the buffer as ‘foo’.
An item can have more than one external link; however, most items have
none at all.
:load fileload, and only if
the file is not already loaded.
:require feature(require 'feature) when your saved customizations
set the value of this item. feature should be a symbol.
The most common reason to use :require is when a variable enables
a feature such as a minor mode, and just setting the variable won't have
any effect unless the code which implements the mode is loaded.
:version version:package-version '(package . version)This keyword takes priority over :version.
package should be the official name of the package, such as MH-E
or Gnus. If the package package is released as part of Emacs,
package and version should appear in the value of
customize-package-emacs-version-alist.
Packages distributed as part of Emacs that use the
:package-version keyword must also update the
customize-package-emacs-version-alist variable.
This alist provides a mapping for the versions of Emacs that are associated with versions of a package listed in the
:package-versionkeyword. Its elements look like this:(package (pversion . eversion)...)For each package, which is a symbol, there are one or more elements that contain a package version pversion with an associated Emacs version eversion. These versions are strings. For example, the MH-E package updates this alist with the following:
(add-to-list 'customize-package-emacs-version-alist '(MH-E ("6.0" . "22.1") ("6.1" . "22.1") ("7.0" . "22.1") ("7.1" . "22.1") ("7.2" . "22.1") ("7.3" . "22.1") ("7.4" . "22.1") ("8.0" . "22.1")))The value of package needs to be unique and it needs to match the package value appearing in the
:package-versionkeyword. Since the user might see the value in a error message, a good choice is the official name of the package, such as MH-E or Gnus.
Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twelve or so options and faces, then you should structure them into subgroups, and put the subgroups under the package's main customization group. It is OK to put some of the options and faces in the package's main group alongside the subgroups.
The package's main or only group should be a member of one or more of
the standard customization groups. (To display the full list of them,
use M-x customize.) Choose one or more of them (but not too
many), and add your group to each of them using the :group
keyword.
The way to declare new customization groups is with defgroup.
Declare group as a customization group containing members. Do not quote the symbol group. The argument doc specifies the documentation string for the group.
The argument members is a list specifying an initial set of customization items to be members of the group. However, most often members is
nil, and you specify the group's members by using the:groupkeyword when defining those members.If you want to specify group members through members, each element should have the form
(name widget). Here name is a symbol, and widget is a widget type for editing that symbol. Useful widgets arecustom-variablefor a variable,custom-facefor a face, andcustom-groupfor a group.When you introduce a new group into Emacs, use the
:versionkeyword in thedefgroup; then you need not use it for the individual members of the group.In addition to the common keywords (see Common Keywords), you can also use this keyword in
defgroup:
The prefix-discarding feature is currently turned off, which means
that :prefix currently has no effect. We did this because we
found that discarding the specified prefixes often led to confusing
names for options. This happened because the people who wrote the
defgroup definitions for various groups added :prefix
keywords whenever they make logical sense—that is, whenever the
variables in the library have a common prefix.
In order to obtain good results with :prefix, it would be
necessary to check the specific effects of discarding a particular
prefix, given the specific items in a group and their names and
documentation. If the resulting text is not clear, then :prefix
should not be used in that case.
It should be possible to recheck all the customization groups, delete
the :prefix specifications which give unclear results, and then
turn this feature back on, if someone would like to do the work.
Use defcustom to declare user-customizable variables.
This macro declares option as a customizable user option. You should not quote option.
This causes the function
user-variable-pto returntwhen given option as an argument. See Defining Variables. The argument doc specifies the documentation string for the variable. (Note that there is no need to start doc with a ‘*’.)The argument standard is an expression that specifies the standard value for option. Evaluating the
defcustomform evaluates standard, but does not necessarily install the standard value. If option already has a default value,defcustomdoes not change it. If the user has saved a customization for option,defcustominstalls the user's customized value as option's default value. If neither of those cases applies,defcustominstalls the result of evaluating standard as the default value.The expression standard can be evaluated at various other times, too—whenever the customization facility needs to know option's standard value. So be sure to use an expression which is harmless to evaluate at any time. We recommend avoiding backquotes in standard, because they are not expanded when editing the value, so list values will appear to have the wrong structure.
Every
defcustomshould specify:groupat least once.If you specify the
:setkeyword, to make the variable take other special actions when set through the customization buffer, the variable's documentation string should tell the user specifically how to do the same job in hand-written Lisp code.When you evaluate a
defcustomform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunarranges to set the variable unconditionally, without testing whether its value is void. (The same feature applies todefvar.) See Defining Variables.If you put a
defcustomin a file that is preloaded at dump time (see Building Emacs), and the standard value installed for the variable at that time might not be correct, usecustom-reevaluate-setting, described below, to re-evaluate the standard value during or after Emacs startup.
defcustom accepts the following additional keywords:
:type type:options value-listThis is meaningful only for certain types, currently including
hook, plist and alist. See the definition of the
individual types for a description of how to use :options.
:set setfunctionset-default.
:get getfunctiondefault-value.
You have to really understand the workings of Custom to use
:get correctly. It is meant for values that are treated in
Custom as variables but are not actually stored in Lisp variables. It
is almost surely a mistake to specify getfunction for a value
that really is stored in a Lisp variable.
:initialize functiondefcustom is evaluated. It should take two arguments,
the option name (a symbol) and the value. Here are some predefined
functions meant for use in this way:
custom-initialize-set:set function to initialize the variable, but
do not reinitialize it if it is already non-void.
custom-initialize-defaultcustom-initialize-set, but use the function
set-default to set the variable, instead of the variable's
:set function. This is the usual choice for a variable whose
:set function enables or disables a minor mode; with this choice,
defining the variable will not call the minor mode function, but
customizing the variable will do so.
custom-initialize-reset:set function to initialize the variable. If
the variable is already non-void, reset it by calling the :set
function using the current value (returned by the :get method).
This is the default :initialize function.
custom-initialize-changed:set function to initialize the variable, if it is
already set or has been customized; otherwise, just use
set-default.
custom-initialize-safe-setcustom-initialize-safe-defaultcustom-initialize-set
(custom-initialize-default, respectively), but catch errors.
If an error occurs during initialization, they set the variable to
nil using set-default, and throw no error.
These two functions are only meant for options defined in pre-loaded files, where some variables or functions used to compute the option's value may not yet be defined. The option normally gets updated in startup.el, ignoring the previously computed value. Because of this typical usage, the value which these two functions compute normally only matters when, after startup, one unsets the option's value and then reevaluates the defcustom. By that time, the necessary variables and functions will be defined, so there will not be an error.
:risky valuerisky-local-variable property to
value (see File Local Variables).
:safe functionsafe-local-variable property to
function (see File Local Variables).
:set-after variables:set-after if setting this variable won't work properly unless
those other variables already have their intended values.
It is useful to specify the :require keyword for an option
that “turns on” a certain feature. This causes Emacs to load the
feature, if it is not already loaded, whenever the option is set.
See Common Keywords. Here is an example, from the library
saveplace.el:
(defcustom save-place nil
"Non-nil means automatically save place in each file..."
:type 'boolean
:require 'saveplace
:group 'save-place)
If a customization item has a type such as hook or
alist, which supports :options, you can add additional
values to the list from outside the defcustom declaration by
calling custom-add-frequent-value. For example, if you define a
function my-lisp-mode-initialization intended to be called from
emacs-lisp-mode-hook, you might want to add that to the list of
reasonable values for emacs-lisp-mode-hook, but not by editing
its definition. You can do it thus:
(custom-add-frequent-value 'emacs-lisp-mode-hook
'my-lisp-mode-initialization)
For the customization option symbol, add value to the list of reasonable values.
The precise effect of adding a value depends on the customization type of symbol.
Internally, defcustom uses the symbol property
standard-value to record the expression for the standard value,
saved-value to record the value saved by the user with the
customization buffer, and customized-value to record the value
set by the user with the customization buffer, but not saved.
See Property Lists. These properties are lists, the car of which
is an expression that evaluates to the value.
This function re-evaluates the standard value of symbol, which should be a user option declared via
defcustom. (If the variable was customized, this function re-evaluates the saved value instead.) This is useful for customizable options that are defined before their value could be computed correctly, such as variables defined in packages that are loaded at dump time, but depend on the run-time information. For example, the value could be a file whose precise name depends on the hierarchy of files when Emacs runs, or a name of a program that needs to be searched at run time.A good place to put calls to this function is in the function
command-linethat is run during startup (see Startup Summary) or in the various hooks it calls.
When you define a user option with defcustom, you must specify
its customization type. That is a Lisp object which describes (1)
which values are legitimate and (2) how to display the value in the
customization buffer for editing.
You specify the customization type in defcustom with the
:type keyword. The argument of :type is evaluated, but
only once when the defcustom is executed, so it isn't useful
for the value to vary. Normally we use a quoted constant. For
example:
(defcustom diff-command "diff"
"The command to use to run diff."
:type '(string)
:group 'diff)
In general, a customization type is a list whose first element is a symbol, one of the customization type names defined in the following sections. After this symbol come a number of arguments, depending on the symbol. Between the type symbol and its arguments, you can optionally write keyword-value pairs (see Type Keywords).
Some type symbols do not use any arguments; those are called
simple types. For a simple type, if you do not use any
keyword-value pairs, you can omit the parentheses around the type
symbol. For example just string as a customization type is
equivalent to (string).
All customization types are implemented as widgets; see Introduction, for details.
This section describes all the simple customization types.
sexpsexp as a fall-back for any option, if you don't want to
take the time to work out a more specific type to use.
integernumberfloatstringregexpstring except that the string must be a valid regular
expression.
characterfile(file :must-match t)directoryhook:options keyword in a hook variable's
defcustom to specify a list of functions recommended for use in
the hook; see Variable Definitions.
alistYou can specify the key and value types like this:
(alist :key-type key-type :value-type value-type)
where key-type and value-type are customization type
specifications. The default key type is sexp, and the default
value type is sexp.
The user can add any key matching the specified key type, but you can
give some keys a preferential treatment by specifying them with the
:options (see Variable Definitions). The specified keys
will always be shown in the customize buffer (together with a suitable
value), with a checkbox to include or exclude or disable the key/value
pair from the alist. The user will not be able to edit the keys
specified by the :options keyword argument.
The argument to the :options keywords should be a list of
specifications for reasonable keys in the alist. Ordinarily, they are
simply atoms, which stand for themselves as. For example:
:options '("foo" "bar" "baz")
specifies that there are three “known” keys, namely "foo",
"bar" and "baz", which will always be shown first.
You may want to restrict the value type for specific keys, for
example, the value associated with the "bar" key can only be an
integer. You can specify this by using a list instead of an atom in
the list. The first element will specify the key, like before, while
the second element will specify the value type. For example:
:options '("foo" ("bar" integer) "baz")
Finally, you may want to change how the key is presented. By default,
the key is simply shown as a const, since the user cannot change
the special keys specified with the :options keyword. However,
you may want to use a more specialized type for presenting the key, like
function-item if you know it is a symbol with a function binding.
This is done by using a customization type specification instead of a
symbol for the key.
:options '("foo" ((function-item some-function) integer)
"baz")
Many alists use lists with two elements, instead of cons cells. For example,
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE).")
instead of
(defcustom cons-alist '(("foo" . 1) ("bar" . 2) ("baz" . 3))
"Each element is a cons-cell (KEY . VALUE).")
Because of the way lists are implemented on top of cons cells, you can
treat list-alist in the example above as a cons cell alist, where
the value type is a list with a single element containing the real
value.
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE)."
:type '(alist :value-type (group integer)))
The group widget is used here instead of list only because
the formatting is better suited for the purpose.
Similarly, you can have alists with more values associated with each key, using variations of this trick:
(defcustom person-data '(("brian" 50 t)
("dorith" 55 nil)
("ken" 52 t))
"Alist of basic info about people.
Each element has the form (NAME AGE MALE-FLAG)."
:type '(alist :value-type (group integer boolean)))
(defcustom pets '(("brian")
("dorith" "dog" "guppy")
("ken" "cat"))
"Alist of people's pets.
In an element (KEY . VALUE), KEY is the person's name,
and the VALUE is a list of that person's pets."
:type '(alist :value-type (repeat string)))
plistplist custom type is similar to the alist (see above),
except that the information is stored as a property list, i.e. a list of
this form:
(key value key value key value ...)
The default :key-type for plist is symbol,
rather than sexp.
symbolfunctionvariablefacebooleannil or t. Note that by
using choice and const together (see the next section),
you can specify that the value must be nil or t, but also
specify the text to describe each value in a way that fits the specific
meaning of the alternative.
coding-systemcolorWhen none of the simple types is appropriate, you can use composite types, which build new types from other types or from specified data. The specified types or data are called the arguments of the composite type. The composite type normally looks like this:
(constructor arguments...)
but you can also add keyword-value pairs before the arguments, like this:
(constructor {keyword value}... arguments...)
Here is a table of constructors and how to use them to write composite types:
(cons car-type cdr-type)(cons string
symbol) is a customization type which matches values such as
("foo" . foo).
In the customization buffer, the car and the cdr are
displayed and edited separately, each according to the type
that you specify for it.
(list element-types...)For example, (list integer string function) describes a list of
three elements; the first element must be an integer, the second a
string, and the third a function.
In the customization buffer, each element is displayed and edited
separately, according to the type specified for it.
(group element-types...)list except for the formatting
of text in the Custom buffer. list labels each
element value with its tag; group does not.
(vector element-types...)list except that the value must be a vector instead of a
list. The elements work the same as in list.
(choice alternative-types...)(choice integer string) allows either an
integer or a string.
In the customization buffer, the user selects an alternative using a menu, and can then edit the value in the usual way for that alternative.
Normally the strings in this menu are determined automatically from the
choices; however, you can specify different strings for the menu by
including the :tag keyword in the alternatives. For example, if
an integer stands for a number of spaces, while a string is text to use
verbatim, you might write the customization type this way,
(choice (integer :tag "Number of spaces")
(string :tag "Literal text"))
so that the menu offers ‘Number of spaces’ and ‘Literal text’.
In any alternative for which nil is not a valid value, other than
a const, you should specify a valid default for that alternative
using the :value keyword. See Type Keywords.
If some values are covered by more than one of the alternatives, customize will choose the first alternative that the value fits. This means you should always list the most specific types first, and the most general last. Here's an example of proper usage:
(choice (const :tag "Off" nil)
symbol (sexp :tag "Other"))
This way, the special value nil is not treated like other
symbols, and symbols are not treated like other Lisp expressions.
(radio element-types...)choice, except that the choices are displayed
using `radio buttons' rather than a menu. This has the advantage of
displaying documentation for the choices when applicable and so is often
a good choice for a choice between constant functions
(function-item customization types).
(const value)The main use of const is inside of choice. For example,
(choice integer (const nil)) allows either an integer or
nil.
:tag is often used with const, inside of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(const :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and foo means “ask.”
(other value)The main use of other is as the last element of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(other :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and anything else means “ask.” If the user chooses ‘Ask’ from
the menu of alternatives, that specifies the value foo; but any
other value (not t, nil or foo) displays as
‘Ask’, just like foo.
(function-item function)const, but used for values which are functions. This
displays the documentation string as well as the function name.
The documentation string is either the one you specify with
:doc, or function's own documentation string.
(variable-item variable)const, but used for values which are variable names. This
displays the documentation string as well as the variable name. The
documentation string is either the one you specify with :doc, or
variable's own documentation string.
(set types...)This appears in the customization buffer as a checklist, so that each of
types may have either one corresponding element or none. It is
not possible to specify two different elements that match the same one
of types. For example, (set integer symbol) allows one
integer and/or one symbol in the list; it does not allow multiple
integers or multiple symbols. As a result, it is rare to use
nonspecific types such as integer in a set.
Most often, the types in a set are const types, as
shown here:
(set (const :bold) (const :italic))
Sometimes they describe possible elements in an alist:
(set (cons :tag "Height" (const height) integer)
(cons :tag "Width" (const width) integer))
That lets the user specify a height value optionally
and a width value optionally.
(repeat element-type)(restricted-sexp :match-alternatives criteria)nil or non-nil according to
the argument. Using a predicate in the list says that objects for which
the predicate returns non-nil are acceptable.
'object. This sort of element
in the list says that object itself is an acceptable value.
For example,
(restricted-sexp :match-alternatives
(integerp 't 'nil))
allows integers, t and nil as legitimate values.
The customization buffer shows all legitimate values using their read syntax, and the user edits them textually.
Here is a table of the keywords you can use in keyword-value pairs in a composite type:
:tag tagchoice.
:match-alternatives criteriarestricted-sexp.
:args argument-list(const :args (foo)) is equivalent to
(const foo). You rarely need to write :args explicitly,
because normally the arguments are recognized automatically as
whatever follows the last keyword-value pair.
The :inline feature lets you splice a variable number of
elements into the middle of a list or vector. You use it in a
set, choice or repeat type which appears among the
element-types of a list or vector.
Normally, each of the element-types in a list or vector
describes one and only one element of the list or vector. Thus, if an
element-type is a repeat, that specifies a list of unspecified
length which appears as one element.
But when the element-type uses :inline, the value it matches is
merged directly into the containing sequence. For example, if it
matches a list with three elements, those become three elements of the
overall sequence. This is analogous to using ‘,@’ in the backquote
construct.
For example, to specify a list whose first element must be baz
and whose remaining arguments should be zero or more of foo and
bar, use this customization type:
(list (const baz) (set :inline t (const foo) (const bar)))
This matches values such as (baz), (baz foo), (baz bar)
and (baz foo bar).
When the element-type is a choice, you use :inline not
in the choice itself, but in (some of) the alternatives of the
choice. For example, to match a list which must start with a
file name, followed either by the symbol t or two strings, use
this customization type:
(list file
(choice (const t)
(list :inline t string string)))
If the user chooses the first alternative in the choice, then the
overall list has two elements and the second element is t. If
the user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.
You can specify keyword-argument pairs in a customization type after the type name symbol. Here are the keywords you can use, and their meanings:
:value defaultchoice; it specifies the default value to use, at first, if and
when the user selects this alternative with the menu in the
customization buffer.
Of course, if the actual value of the option fits this alternative, it will appear showing the actual value, not default.
If nil is not a valid value for the alternative, then it is
essential to specify a valid default with :value.
:format format-string:action
attribute specifies what the button will do if the user invokes it;
its value is a function which takes two arguments—the widget which
the button appears in, and the event.
There is no way to specify two different buttons with different
actions.
:sample-face.
:tag
keyword.
:action action:button-face face:button-prefix prefix:button-suffix suffixnil:tag tag:doc doc:format, and use ‘%d’ or ‘%h’
in that value.
The usual reason to specify a documentation string for a type is to
provide more information about the meanings of alternatives inside a
:choice type or the parts of some other composite type.
:help-echo motion-docwidget-forward or
widget-backward, it will display the string motion-doc in
the echo area. In addition, motion-doc is used as the mouse
help-echo string and may actually be a function or form evaluated
to yield a help string. If it is a function, it is called with one
argument, the widget.
:match functionnil if
the value is acceptable.
:validate functionnil if the widget's
current value is valid for the widget. Otherwise, it should return
the widget containing the invalid data, and set that widget's
:error property to a string explaining the error.
In the previous sections we have described how to construct elaborate
type specifications for defcustom. In some cases you may want
to give such a type specification a name. The obvious case is when
you are using the same type for many user options: rather than repeat
the specification for each option, you can give the type specification
a name, and use that name each defcustom. The other case is
when a user option's value is a recursive data structure. To make it
possible for a datatype to refer to itself, it needs to have a name.
Since custom types are implemented as widgets, the way to define a new customize type is to define a new widget. We are not going to describe the widget interface here in details, see Introduction, for that. Instead we are going to demonstrate the minimal functionality needed for defining new customize types by a simple example.
(define-widget 'binary-tree-of-string 'lazy
"A binary tree made of cons-cells and strings."
:offset 4
:tag "Node"
:type '(choice (string :tag "Leaf" :value "")
(cons :tag "Interior"
:value ("" . "")
binary-tree-of-string
binary-tree-of-string)))
(defcustom foo-bar ""
"Sample variable holding a binary tree of strings."
:type 'binary-tree-of-string)
The function to define a new widget is called define-widget. The
first argument is the symbol we want to make a new widget type. The
second argument is a symbol representing an existing widget, the new
widget is going to be defined in terms of difference from the existing
widget. For the purpose of defining new customization types, the
lazy widget is perfect, because it accepts a :type keyword
argument with the same syntax as the keyword argument to
defcustom with the same name. The third argument is a
documentation string for the new widget. You will be able to see that
string with the M-x widget-browse <RET> binary-tree-of-string
<RET> command.
After these mandatory arguments follow the keyword arguments. The most
important is :type, which describes the data type we want to match
with this widget. Here a binary-tree-of-string is described as
being either a string, or a cons-cell whose car and cdr are themselves
both binary-tree-of-string. Note the reference to the widget
type we are currently in the process of defining. The :tag
attribute is a string to name the widget in the user interface, and the
:offset argument is there to ensure that child nodes are
indented four spaces relative to the parent node, making the tree
structure apparent in the customization buffer.
The defcustom shows how the new widget can be used as an ordinary
customization type.
The reason for the name lazy is that the other composite
widgets convert their inferior widgets to internal form when the
widget is instantiated in a buffer. This conversion is recursive, so
the inferior widgets will convert their inferior widgets. If
the data structure is itself recursive, this conversion is an infinite
recursion. The lazy widget prevents the recursion: it convert
its :type argument only when needed.
Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file.
The load functions evaluate all the expressions in a file just
as the eval-buffer function evaluates all the
expressions in a buffer. The difference is that the load functions
read and evaluate the text in the file as found on disk, not the text
in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions.
A file containing Lisp code is often called a library. Thus, the “Rmail library” is a file containing code for Rmail mode. Similarly, a “Lisp library directory” is a directory of files containing Lisp code.
Emacs Lisp has several interfaces for loading. For example,
autoload creates a placeholder object for a function defined in a
file; trying to call the autoloading function loads the file to get the
function's real definition (see Autoload). require loads a
file if it isn't already loaded (see Named Features). Ultimately,
all these facilities call the load function to do the work.
This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file.
To find the file,
loadfirst looks for a file named filename.elc, that is, for a file whose name is filename with the extension ‘.elc’ appended. If such a file exists, it is loaded. If there is no file by that name, thenloadlooks for a file named filename.el. If that file exists, it is loaded. Finally, if neither of those names is found,loadlooks for a file named filename with nothing appended, and loads it if it exists. (Theloadfunction is not clever about looking at filename. In the perverse case of a file named foo.el.el, evaluation of(load "foo.el")will indeed find it.)If Auto Compression mode is enabled, as it is by default, then if
loadcan not find a file, it searches for a compressed version of the file before trying other file names. It decompresses and loads it if it exists. It looks for compressed versions by appending each of the suffixes injka-compr-load-suffixesto the file name. The value of this variable must be a list of strings. Its standard value is(".gz").If the optional argument nosuffix is non-
nil, thenloaddoes not try the suffixes ‘.elc’ and ‘.el’. In this case, you must specify the precise file name you want, except that, if Auto Compression mode is enabled,loadwill still usejka-compr-load-suffixesto find compressed versions. By specifying the precise file name and usingtfor nosuffix, you can prevent perverse file names such as foo.el.el from being tried.If the optional argument must-suffix is non-
nil, thenloadinsists that the file name used must end in either ‘.el’ or ‘.elc’ (possibly extended with a compression suffix), unless it contains an explicit directory name.If filename is a relative file name, such as foo or baz/foo.bar,
loadsearches for the file using the variableload-path. It appends filename to each of the directories listed inload-path, and loads the first file it finds whose name matches. The current default directory is tried only if it is specified inload-path, wherenilstands for the default directory.loadtries all three possible suffixes in the first directory inload-path, then all three suffixes in the second directory, and so on. See Library Search.Whatever the name under which the file is eventually found, and the directory where Emacs found it, Emacs sets the value of the variable
load-file-nameto that file's name.If you get a warning that foo.elc is older than foo.el, it means you should consider recompiling foo.el. See Byte Compilation.
When loading a source file (not compiled),
loadperforms character set translation just as Emacs would do when visiting the file. See Coding Systems.Messages like ‘Loading foo...’ and ‘Loading foo...done’ appear in the echo area during loading unless nomessage is non-
nil.Any unhandled errors while loading a file terminate loading. If the load was done for the sake of
autoload, any function definitions made during the loading are undone.If
loadcan't find the file to load, then normally it signals the errorfile-error(with ‘Cannot open load file filename’). But if missing-ok is non-nil, thenloadjust returnsnil.You can use the variable
load-read-functionto specify a function forloadto use instead ofreadfor reading expressions. See below.
loadreturnstif the file loads successfully.
This command loads the file filename. If filename is a relative file name, then the current default directory is assumed. This command does not use
load-path, and does not append suffixes. However, it does look for compressed versions (if Auto Compression Mode is enabled). Use this command if you wish to specify precisely the file name to load.
This command loads the library named library. It is equivalent to
load, except for the way it reads its argument interactively. See Lisp Libraries.
This variable is non-
nilif Emacs is in the process of loading a file, and it isnilotherwise.
When Emacs is in the process of loading a file, this variable's value is the name of that file, as Emacs found it during the search described earlier in this section.
This variable specifies an alternate expression-reading function for
loadandeval-regionto use instead ofread. The function should accept one argument, just asreaddoes.Normally, the variable's value is
nil, which means those functions should useread.Instead of using this variable, it is cleaner to use another, newer feature: to pass the function as the read-function argument to
eval-region. See Eval.
For information about how load is used in building Emacs, see
Building Emacs.
We now describe some technical details about the exact suffixes that
load tries.
This is a list of suffixes indicating (compiled or source) Emacs Lisp files. It should not include the empty string.
loaduses these suffixes in order when it appends Lisp suffixes to the specified file name. The standard value is(".elc" ".el")which produces the behavior described in the previous section.
This is a list of suffixes that indicate representations of the same file. This list should normally start with the empty string. When
loadsearches for a file it appends the suffixes in this list, in order, to the file name, before searching for another file.Enabling Auto Compression mode appends the suffixes in
jka-compr-load-suffixesto this list and disabling Auto Compression mode removes them again. The standard value ofload-file-rep-suffixesif Auto Compression mode is disabled is(""). Given that the standard value ofjka-compr-load-suffixesis(".gz"), the standard value ofload-file-rep-suffixesif Auto Compression mode is enabled is("" ".gz").
This function returns the list of all suffixes that
loadshould try, in order, when its must-suffix argument is non-nil. This takes bothload-suffixesandload-file-rep-suffixesinto account. Ifload-suffixes,jka-compr-load-suffixesandload-file-rep-suffixesall have their standard values, this function returns(".elc" ".elc.gz" ".el" ".el.gz")if Auto Compression mode is enabled and(".elc" ".el")if Auto Compression mode is disabled.
To summarize, load normally first tries the suffixes in the
value of (get-load-suffixes) and then those in
load-file-rep-suffixes. If nosuffix is non-nil,
it skips the former group, and if must-suffix is non-nil,
it skips the latter group.
When Emacs loads a Lisp library, it searches for the library
in a list of directories specified by the variable load-path.
The value of this variable is a list of directories to search when loading files with
load. Each element is a string (which must be a directory name) ornil(which stands for the current working directory).
The value of load-path is initialized from the environment
variable EMACSLOADPATH, if that exists; otherwise its default
value is specified in emacs/src/epaths.h when Emacs is built.
Then the list is expanded by adding subdirectories of the directories
in the list.
The syntax of EMACSLOADPATH is the same as used for PATH;
‘:’ (or ‘;’, according to the operating system) separates
directory names, and ‘.’ is used for the current default directory.
Here is an example of how to set your EMACSLOADPATH variable from
a csh .login file:
setenv EMACSLOADPATH .:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is how to set it using sh:
export EMACSLOADPATH
EMACSLOADPATH=.:/user/bil/emacs:/usr/local/share/emacs/20.3/lisp
Here is an example of code you can place in your init file (see Init File) to add several directories to the front of your default
load-path:
(setq load-path
(append (list nil "/user/bil/emacs"
"/usr/local/lisplib"
"~/emacs")
load-path))
In this example, the path searches the current working directory first, followed then by the /user/bil/emacs directory, the /usr/local/lisplib directory, and the ~/emacs directory, which are then followed by the standard directories for Lisp code.
Dumping Emacs uses a special value of load-path. If the value of
load-path at the end of dumping is unchanged (that is, still the
same special value), the dumped Emacs switches to the ordinary
load-path value when it starts up, as described above. But if
load-path has any other value at the end of dumping, that value
is used for execution of the dumped Emacs also.
Therefore, if you want to change load-path temporarily for
loading a few libraries in site-init.el or site-load.el,
you should bind load-path locally with let around the
calls to load.
The default value of load-path, when running an Emacs which has
been installed on the system, includes two special directories (and
their subdirectories as well):
"/usr/local/share/emacs/version/site-lisp"
and
"/usr/local/share/emacs/site-lisp"
The first one is for locally installed packages for a particular Emacs version; the second is for locally installed packages meant for use with all installed Emacs versions.
There are several reasons why a Lisp package that works well in one Emacs version can cause trouble in another. Sometimes packages need updating for incompatible changes in Emacs; sometimes they depend on undocumented internal Emacs data that can change without notice; sometimes a newer Emacs version incorporates a version of the package, and should be used only with that version.
Emacs finds these directories' subdirectories and adds them to
load-path when it starts up. Both immediate subdirectories and
subdirectories multiple levels down are added to load-path.
Not all subdirectories are included, though. Subdirectories whose names do not start with a letter or digit are excluded. Subdirectories named RCS or CVS are excluded. Also, a subdirectory which contains a file named .nosearch is excluded. You can use these methods to prevent certain subdirectories of the site-lisp directories from being searched.
If you run Emacs from the directory where it was built—that is, an
executable that has not been formally installed—then load-path
normally contains two additional directories. These are the lisp
and site-lisp subdirectories of the main build directory. (Both
are represented as absolute file names.)
This command finds the precise file name for library library. It searches for the library in the same way
loaddoes, and the argument nosuffix has the same meaning as inload: don't add suffixes ‘.elc’ or ‘.el’ to the specified name library.If the path is non-
nil, that list of directories is used instead ofload-path.When
locate-libraryis called from a program, it returns the file name as a string. When the user runslocate-libraryinteractively, the argument interactive-call ist, and this tellslocate-libraryto display the file name in the echo area.
This command shows a list of shadowed Emacs Lisp files. A shadowed file is one that will not normally be loaded, despite being in a directory on
load-path, due to the existence of another similarly-named file in a directory earlier onload-path.For instance, suppose
load-pathis set to("/opt/emacs/site-lisp" "/usr/share/emacs/23.3/lisp")and that both these directories contain a file named foo.el. Then
(require 'foo)never loads the file in the second directory. Such a situation might indicate a problem in the way Emacs was installed.When called from Lisp, this function prints a message listing the shadowed files, instead of displaying them in a buffer. If the optional argument
stringpis non-nil, it instead returns the shadowed files as a string.
When Emacs Lisp programs contain string constants with non-ASCII characters, these can be represented within Emacs either as unibyte strings or as multibyte strings (see Text Representations). Which representation is used depends on how the file is read into Emacs. If it is read with decoding into multibyte representation, the text of the Lisp program will be multibyte text, and its string constants will be multibyte strings. If a file containing Latin-1 characters (for example) is read without decoding, the text of the program will be unibyte text, and its string constants will be unibyte strings. See Coding Systems.
To make the results more predictable, Emacs always performs decoding into the multibyte representation when loading Lisp files, even if it was started with the ‘--unibyte’ option. This means that string constants with non-ASCII characters translate into multibyte strings. The only exception is when a particular file specifies no decoding.
The reason Emacs is designed this way is so that Lisp programs give predictable results, regardless of how Emacs was started. In addition, this enables programs that depend on using multibyte text to work even in a unibyte Emacs.
In most Emacs Lisp programs, the fact that non-ASCII strings are
multibyte strings should not be noticeable, since inserting them in
unibyte buffers converts them to unibyte automatically. However, if
this does make a difference, you can force a particular Lisp file to be
interpreted as unibyte by writing ‘-*-unibyte: t;-*-’ in a
comment on the file's first line. With that designator, the file will
unconditionally be interpreted as unibyte, even in an ordinary
multibyte Emacs session. This can matter when making keybindings to
non-ASCII characters written as ?vliteral.
The autoload facility allows you to make a function or macro known in Lisp, but put off loading the file that defines it. The first call to the function automatically reads the proper file to install the real definition and other associated code, then runs the real definition as if it had been loaded all along.
There are two ways to set up an autoloaded function: by calling
autoload, and by writing a special “magic” comment in the
source before the real definition. autoload is the low-level
primitive for autoloading; any Lisp program can call autoload at
any time. Magic comments are the most convenient way to make a function
autoload, for packages installed along with Emacs. These comments do
nothing on their own, but they serve as a guide for the command
update-file-autoloads, which constructs calls to autoload
and arranges to execute them when Emacs is built.
This function defines the function (or macro) named function so as to load automatically from filename. The string filename specifies the file to load to get the real definition of function.
If filename does not contain either a directory name, or the suffix
.elor.elc, thenautoloadinsists on adding one of these suffixes, and it will not load from a file whose name is just filename with no added suffix. (The variableload-suffixesspecifies the exact required suffixes.)The argument docstring is the documentation string for the function. Specifying the documentation string in the call to
autoloadmakes it possible to look at the documentation without loading the function's real definition. Normally, this should be identical to the documentation string in the function definition itself. If it isn't, the function definition's documentation string takes effect when it is loaded.If interactive is non-
nil, that says function can be called interactively. This lets completion in M-x work without loading function's real definition. The complete interactive specification is not given here; it's not needed unless the user actually calls function, and when that happens, it's time to load the real definition.You can autoload macros and keymaps as well as ordinary functions. Specify type as
macroif function is really a macro. Specify type askeymapif function is really a keymap. Various parts of Emacs need to know this information without loading the real definition.An autoloaded keymap loads automatically during key lookup when a prefix key's binding is the symbol function. Autoloading does not occur for other kinds of access to the keymap. In particular, it does not happen when a Lisp program gets the keymap from the value of a variable and calls
define-key; not even if the variable name is the same symbol function.If function already has a non-void function definition that is not an autoload object,
autoloaddoes nothing and returnsnil. If the function cell of function is void, or is already an autoload object, then it is defined as an autoload object like this:(autoload filename docstring interactive type)For example,
(symbol-function 'run-prolog) ⇒ (autoload "prolog" 169681 t nil)In this case,
"prolog"is the name of the file to load, 169681 refers to the documentation string in the emacs/etc/DOC-version file (see Documentation Basics),tmeans the function is interactive, andnilthat it is not a macro or a keymap.
The autoloaded file usually contains other definitions and may require
or provide one or more features. If the file is not completely loaded
(due to an error in the evaluation of its contents), any function
definitions or provide calls that occurred during the load are
undone. This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file. If not for
this, then some of the functions in the file might be defined by the
aborted load, but fail to work properly for the lack of certain
subroutines not loaded successfully because they come later in the file.
If the autoloaded file fails to define the desired Lisp function or
macro, then an error is signaled with data "Autoloading failed to
define function function-name".
A magic autoload comment (often called an autoload cookie)
consists of ‘;;;###autoload’, on a line by itself,
just before the real definition of the function in its
autoloadable source file. The command M-x update-file-autoloads
writes a corresponding autoload call into loaddefs.el.
(The string that serves as the autoload cookie and the name of the
file generated by update-file-autoloads can be changed from the
above defaults, see below.)
Building Emacs loads loaddefs.el and thus calls autoload.
M-x update-directory-autoloads is even more powerful; it updates
autoloads for all files in the current directory.
The same magic comment can copy any kind of form into
loaddefs.el. If the form following the magic comment is not a
function-defining form or a defcustom form, it is copied
verbatim. “Function-defining forms” include define-skeleton,
define-derived-mode, define-generic-mode and
define-minor-mode as well as defun and
defmacro. To save space, a defcustom form is converted to
a defvar in loaddefs.el, with some additional information
if it uses :require.
You can also use a magic comment to execute a form at build time without executing it when the file itself is loaded. To do this, write the form on the same line as the magic comment. Since it is in a comment, it does nothing when you load the source file; but M-x update-file-autoloads copies it to loaddefs.el, where it is executed while building Emacs.
The following example shows how doctor is prepared for
autoloading with a magic comment:
;;;###autoload
(defun doctor ()
"Switch to *doctor* buffer and start giving psychotherapy."
(interactive)
(switch-to-buffer "*doctor*")
(doctor-mode))
Here's what that produces in loaddefs.el:
(autoload (quote doctor) "doctor" "\
Switch to *doctor* buffer and start giving psychotherapy.
\(fn)" t nil)
The backslash and newline immediately following the double-quote are a
convention used only in the preloaded uncompiled Lisp files such as
loaddefs.el; they tell make-docfile to put the
documentation string in the etc/DOC file. See Building Emacs.
See also the commentary in lib-src/make-docfile.c. ‘(fn)’
in the usage part of the documentation string is replaced with the
function's name when the various help functions (see Help Functions) display it.
If you write a function definition with an unusual macro that is not
one of the known and recognized function definition methods, use of an
ordinary magic autoload comment would copy the whole definition into
loaddefs.el. That is not desirable. You can put the desired
autoload call into loaddefs.el instead by writing this:
;;;###autoload (autoload 'foo "myfile")
(mydefunmacro foo
...)
You can use a non-default string as the autoload cookie and have the corresponding autoload calls written into a file whose name is different from the default loaddefs.el. Emacs provides two variables to control this:
The value of this variable should be a string whose syntax is a Lisp comment. M-x update-file-autoloads copies the Lisp form that follows the cookie into the autoload file it generates. The default value of this variable is
";;;###autoload".
The value of this variable names an Emacs Lisp file where the autoload calls should go. The default value is loaddefs.el, but you can override that, e.g., in the “Local Variables” section of a .el file (see File Local Variables). The autoload file is assumed to contain a trailer starting with a formfeed character.
You can load a given file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file it came from.
When you load or reload files, bear in mind that the load and
load-library functions automatically load a byte-compiled file
rather than a non-compiled file of similar name. If you rewrite a file
that you intend to save and reinstall, you need to byte-compile the new
version; otherwise Emacs will load the older, byte-compiled file instead
of your newer, non-compiled file! If that happens, the message
displayed when loading the file includes, ‘(compiled; note, source is
newer)’, to remind you to recompile it.
When writing the forms in a Lisp library file, keep in mind that the
file might be loaded more than once. For example, think about whether
each variable should be reinitialized when you reload the library;
defvar does not change the value if the variable is already
initialized. (See Defining Variables.)
The simplest way to add an element to an alist is like this:
(push '(leif-mode " Leif") minor-mode-alist)
But this would add multiple elements if the library is reloaded. To
avoid the problem, use add-to-list (see List Variables):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Occasionally you will want to test explicitly whether a library has
already been loaded. If the library uses provide to provide a
named feature, you can use featurep earlier in the file to test
whether the provide call has been executed before (see Named Features). Alternatively, you could use something like this:
(defvar foo-was-loaded nil)
(unless foo-was-loaded
execute-first-time-only
(setq foo-was-loaded t))
provide and require are an alternative to
autoload for loading files automatically. They work in terms of
named features. Autoloading is triggered by calling a specific
function, but a feature is loaded the first time another program asks
for it by name.
A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should provide the feature. Another program that uses them may ensure they are defined by requiring the feature. This loads the file of definitions if it hasn't been loaded already.
To require the presence of a feature, call require with the
feature name as argument. require looks in the global variable
features to see whether the desired feature has been provided
already. If not, it loads the feature from the appropriate file. This
file should call provide at the top level to add the feature to
features; if it fails to do so, require signals an error.
For example, in emacs/lisp/prolog.el,
the definition for run-prolog includes the following code:
(defun run-prolog ()
"Run an inferior Prolog process, with I/O via buffer *prolog*."
(interactive)
(require 'comint)
(switch-to-buffer (make-comint "prolog" prolog-program-name))
(inferior-prolog-mode))
The expression (require 'comint) loads the file comint.el
if it has not yet been loaded. This ensures that make-comint is
defined. Features are normally named after the files that provide them,
so that require need not be given the file name.
The comint.el file contains the following top-level expression:
(provide 'comint)
This adds comint to the global features list, so that
(require 'comint) will henceforth know that nothing needs to be
done.
When require is used at top level in a file, it takes effect
when you byte-compile that file (see Byte Compilation) as well as
when you load it. This is in case the required package contains macros
that the byte compiler must know about. It also avoids byte compiler
warnings for functions and variables defined in the file loaded with
require.
Although top-level calls to require are evaluated during
byte compilation, provide calls are not. Therefore, you can
ensure that a file of definitions is loaded before it is byte-compiled
by including a provide followed by a require for the same
feature, as in the following example.
(provide 'my-feature) ; Ignored by byte compiler,
; evaluated by load.
(require 'my-feature) ; Evaluated by byte compiler.
The compiler ignores the provide, then processes the
require by loading the file in question. Loading the file does
execute the provide call, so the subsequent require call
does nothing when the file is loaded.
This function announces that feature is now loaded, or being loaded, into the current Emacs session. This means that the facilities associated with feature are or will be available for other Lisp programs.
The direct effect of calling
provideis if not already in features then to add feature to the front of that list and call anyeval-after-loadcode waiting for it (see Hooks for Loading). The argument feature must be a symbol.providereturns feature.If provided, subfeatures should be a list of symbols indicating a set of specific subfeatures provided by this version of feature. You can test the presence of a subfeature using
featurep. The idea of subfeatures is that you use them when a package (which is one feature) is complex enough to make it useful to give names to various parts or functionalities of the package, which might or might not be loaded, or might or might not be present in a given version. See Network Feature Testing, for an example.features ⇒ (bar bish) (provide 'foo) ⇒ foo features ⇒ (foo bar bish)When a file is loaded to satisfy an autoload, and it stops due to an error in the evaluation of its contents, any function definitions or
providecalls that occurred during the load are undone. See Autoload.
This function checks whether feature is present in the current Emacs session (using
(featurepfeature); see below). The argument feature must be a symbol.If the feature is not present, then
requireloads filename withload. If filename is not supplied, then the name of the symbol feature is used as the base file name to load. However, in this case,requireinsists on finding feature with an added ‘.el’ or ‘.elc’ suffix (possibly extended with a compression suffix); a file whose name is just feature won't be used. (The variableload-suffixesspecifies the exact required Lisp suffixes.)If noerror is non-
nil, that suppresses errors from actual loading of the file. In that case,requirereturnsnilif loading the file fails. Normally,requirereturns feature.If loading the file succeeds but does not provide feature,
requiresignals an error, ‘Required feature feature was not provided’.
This function returns
tif feature has been provided in the current Emacs session (i.e., if feature is a member offeatures.) If subfeature is non-nil, then the function returnstonly if that subfeature is provided as well (i.e. if subfeature is a member of thesubfeatureproperty of the feature symbol.)
The value of this variable is a list of symbols that are the features loaded in the current Emacs session. Each symbol was put in this list with a call to
provide. The order of the elements in thefeatureslist is not significant.
This function returns the name of the file that defined symbol. If type is
nil, then any kind of definition is acceptable. If type isdefun,defvar, ordefface, that specifies function definition, variable definition, or face definition only.The value is normally an absolute file name. It can also be
nil, if the definition is not associated with any file. If symbol specifies an autoloaded function, the value can be a relative file name without extension.
The basis for symbol-file is the data in the variable
load-history.
The value of this variable is an alist that associates the names of loaded library files with the names of the functions and variables they defined, as well as the features they provided or required.
Each element in this alist describes one loaded library (including libraries that are preloaded at startup). It is a list whose car is the absolute file name of the library (a string). The rest of the list elements have these forms:
- var
- The symbol var was defined as a variable.
(defun .fun)- The function fun was defined.
(t .fun)- The function fun was previously an autoload before this library redefined it as a function. The following element is always
(defun .fun), which represents defining fun as a function.(autoload .fun)- The function fun was defined as an autoload.
(defface .face)- The face face was defined.
(require .feature)- The feature feature was required.
(provide .feature)- The feature feature was provided.
The value of
load-historymay have one element whose car isnil. This element describes definitions made witheval-bufferon a buffer that is not visiting a file.
The command eval-region updates load-history, but does so
by adding the symbols defined to the element for the file being visited,
rather than replacing that element. See Eval.
You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects. To do this, use the function
unload-feature:
This command unloads the library that provided feature feature. It undefines all functions, macros, and variables defined in that library with
defun,defalias,defsubst,defmacro,defconst,defvar, anddefcustom. It then restores any autoloads formerly associated with those symbols. (Loading saves these in theautoloadproperty of the symbol.)Before restoring the previous definitions,
unload-featurerunsremove-hookto remove functions in the library from certain hooks. These hooks include variables whose names end in ‘hook’ or ‘-hooks’, plus those listed inunload-feature-special-hooks, as well asauto-mode-alist. This is to prevent Emacs from ceasing to function because important hooks refer to functions that are no longer defined.Standard unloading activities also undoes ELP profiling of functions in that library, unprovides any features provided by the library, and cancels timers held in variables defined by the library.
If these measures are not sufficient to prevent malfunction, a library can define an explicit unloader named feature
-unload-function. If that symbol is defined as a function,unload-featurecalls it with no arguments before doing anything else. It can do whatever is appropriate to unload the library. If it returnsnil,unload-featureproceeds to take the normal unload actions. Otherwise it considers the job to be done.Ordinarily,
unload-featurerefuses to unload a library on which other loaded libraries depend. (A library a depends on library b if a contains arequirefor b.) If the optional argument force is non-nil, dependencies are ignored and you can unload any library.
The unload-feature function is written in Lisp; its actions are
based on the variable load-history.
This variable holds a list of hooks to be scanned before unloading a library, to remove functions defined in the library.
You can ask for code to be executed each time Emacs loads a library,
by using the variable after-load-functions:
This abnormal hook is run after loading a file. Each function in the hook is called with a single argument, the absolute filename of the file that was just loaded.
If you want code to be executed when a particular library is
loaded, use the function eval-after-load:
This function arranges to evaluate form at the end of loading the file library, each time library is loaded. If library is already loaded, it evaluates form right away. Don't forget to quote form!
You don't need to give a directory or extension in the file name library. Normally, you just give a bare file name, like this:
(eval-after-load "edebug" '(def-edebug-spec c-point t))To restrict which files can trigger the evaluation, include a directory or an extension or both in library. Only a file whose absolute true name (i.e., the name with all symbolic links chased out) matches all the given name components will match. In the following example, my_inst.elc or my_inst.elc.gz in some directory
..../foo/barwill trigger the evaluation, but not my_inst.el:(eval-after-load "foo/bar/my_inst.elc" ...)library can also be a feature (i.e. a symbol), in which case form is evaluated when
(providelibrary)is called.An error in form does not undo the load, but does prevent execution of the rest of form.
Normally, well-designed Lisp programs should not use
eval-after-load. If you need to examine and set the variables
defined in another library (those meant for outside use), you can do
it immediately—there is no need to wait until the library is loaded.
If you need to call functions defined by that library, you should load
the library, preferably with require (see Named Features).
But it is OK to use eval-after-load in your personal
customizations if you don't feel that they must meet the design
standards for programs meant for wider use.
This variable stores an alist built by
eval-after-load, containing the expressions to evaluate when certain libraries are loaded. Each element looks like this:(regexp-or-feature forms...)The key regexp-or-feature is either a regular expression or a symbol, and the value is a list of forms. The forms are evaluated when the key matches the absolute true name or feature name of the library being loaded.
Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.
Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code.
Compiling a Lisp file with the Emacs byte compiler always reads the file as multibyte text, even if Emacs was started with ‘--unibyte’, unless the file specifies otherwise. This is so that compilation gives results compatible with running the same file without compilation. See Loading Non-ASCII.
In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true.
If you do not want a Lisp file to be compiled, ever, put a file-local
variable binding for no-byte-compile into it, like this:
;; -*-no-byte-compile: t; -*-
See Compilation Errors, for how to investigate errors occurring in byte compilation.
A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
⇒ silly-loop
(silly-loop 50000000)
⇒ ("Wed Mar 11 21:10:19 2009"
"Wed Mar 11 21:10:41 2009") ; 22 seconds
(byte-compile 'silly-loop)
⇒ [Compiled code not shown]
(silly-loop 50000000)
⇒ ("Wed Mar 11 21:12:26 2009"
"Wed Mar 11 21:12:32 2009") ; 6 seconds
In this example, the interpreted code required 22 seconds to run, whereas the byte-compiled code required 6 seconds. These results are representative, but actual results will vary greatly.
You can byte-compile an individual function or macro definition with
the byte-compile function. You can compile a whole file with
byte-compile-file, or several files with
byte-recompile-directory or batch-byte-compile.
The byte compiler produces error messages and warnings about each file in a buffer called ‘*Compile-Log*’. These report things in your program that suggest a problem but are not necessarily erroneous.
Be careful when writing macro calls in files that you may someday
byte-compile. Macro calls are expanded when they are compiled, so the
macros must already be defined for proper compilation. For more
details, see Compiling Macros. If a program does not work the
same way when compiled as it does when interpreted, erroneous macro
definitions are one likely cause (see Problems with Macros).
Inline (defsubst) functions are less troublesome; if you
compile a call to such a function before its definition is known, the
call will still work right, it will just run slower.
Normally, compiling a file does not evaluate the file's contents or
load the file. But it does execute any require calls at top
level in the file. One way to ensure that necessary macro definitions
are available during compilation is to require the file that defines
them (see Named Features). To avoid loading the macro definition files
when someone runs the compiled program, write
eval-when-compile around the require calls (see Eval During Compile).
This function byte-compiles the function definition of symbol, replacing the previous definition with the compiled one. The function definition of symbol must be the actual code for the function; i.e., the compiler does not follow indirection to another symbol.
byte-compilereturns the new, compiled definition of symbol.If symbol's definition is a byte-code function object,
byte-compiledoes nothing and returnsnil. Lisp records only one function definition for any symbol, and if that is already compiled, non-compiled code is not available anywhere. So there is no way to “compile the same definition again.”(defun factorial (integer) "Compute factorial of INTEGER." (if (= 1 integer) 1 (* integer (factorial (1- integer))))) ⇒ factorial (byte-compile 'factorial) ⇒ #[(integer) "^H\301U\203^H^@\301\207\302^H\303^HS!\"\207" [integer 1 * factorial] 4 "Compute factorial of INTEGER."]The result is a byte-code function object. The string it contains is the actual byte-code; each character in it is an instruction or an operand of an instruction. The vector contains all the constants, variable names and function names used by the function, except for certain primitives that are coded as special instructions.
If the argument to
byte-compileis alambdaexpression, it returns the corresponding compiled code, but does not store it anywhere.
This command reads the defun containing point, compiles it, and evaluates the result. If you use this on a defun that is actually a function definition, the effect is to install a compiled version of that function.
compile-defunnormally displays the result of evaluation in the echo area, but if arg is non-nil, it inserts the result in the current buffer after the form it compiled.
This function compiles a file of Lisp code named filename into a file of byte-code. The output file's name is made by changing the ‘.el’ suffix into ‘.elc’; if filename does not end in ‘.el’, it adds ‘.elc’ to the end of filename.
Compilation works by reading the input file one form at a time. If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read.
This command returns
tif there were no errors andnilotherwise. When called interactively, it prompts for the file name.If load is non-
nil, this command loads the compiled file after compiling it. Interactively, load is the prefix argument.% ls -l push* -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el (byte-compile-file "~/emacs/push.el") ⇒ t % ls -l push* -rw-r--r-- 1 lewis 791 Oct 5 20:31 push.el -rw-rw-rw- 1 lewis 638 Oct 8 20:25 push.elc
This command recompiles every ‘.el’ file in directory (or its subdirectories) that needs recompilation. A file needs recompilation if a ‘.elc’ file exists but is older than the ‘.el’ file.
When a ‘.el’ file has no corresponding ‘.elc’ file, flag says what to do. If it is
nil, this command ignores these files. If flag is 0, it compiles them. If it is neithernilnor 0, it asks the user whether to compile each such file, and asks about each subdirectory as well.Interactively,
byte-recompile-directoryprompts for directory and flag is the prefix argument.If force is non-
nil, this command recompiles every ‘.el’ file that has a ‘.elc’ file.The returned value is unpredictable.
This function runs
byte-compile-fileon files specified on the command line. This function must be used only in a batch execution of Emacs, as it kills Emacs on completion. An error in one file does not prevent processing of subsequent files, but no output file will be generated for it, and the Emacs process will terminate with a nonzero status code.If noforce is non-
nil, this function does not recompile files that have an up-to-date ‘.elc’ file.% emacs -batch -f batch-byte-compile *.el
This function actually interprets byte-code. A byte-compiled function is actually defined with a body that calls
byte-code. Don't call this function yourself—only the byte compiler knows how to generate valid calls to this function.In Emacs version 18, byte-code was always executed by way of a call to the function
byte-code. Nowadays, byte-code is usually executed as part of a byte-code function object, and only rarely through an explicit call tobyte-code.
Functions and variables loaded from a byte-compiled file access their documentation strings dynamically from the file whenever needed. This saves space within Emacs, and makes loading faster because the documentation strings themselves need not be processed while loading the file. Actual access to the documentation strings becomes slower as a result, but this normally is not enough to bother users.
Dynamic access to documentation strings does have drawbacks:
If your site installs Emacs following the usual procedures, these problems will never normally occur. Installing a new version uses a new directory with a different name; as long as the old version remains installed, its files will remain unmodified in the places where they are expected to be.
However, if you have built Emacs yourself and use it from the directory where you built it, you will experience this problem occasionally if you edit and recompile Lisp files. When it happens, you can cure the problem by reloading the file after recompiling it.
You can turn off this feature at compile time by setting
byte-compile-dynamic-docstrings to nil; this is useful
mainly if you expect to change the file, and you want Emacs processes
that have already loaded it to keep working when the file changes.
You can do this globally, or for one source file by specifying a
file-local binding for the variable. One way to do that is by adding
this string to the file's first line:
-*-byte-compile-dynamic-docstrings: nil;-*-
If this is non-
nil, the byte compiler generates compiled files that are set up for dynamic loading of documentation strings.
The dynamic documentation string feature writes compiled files that use a special Lisp reader construct, ‘#@count’. This construct skips the next count characters. It also uses the ‘#$’ construct, which stands for “the name of this file, as a string.” It is usually best not to use these constructs in Lisp source files, since they are not designed to be clear to humans reading the file.
When you compile a file, you can optionally enable the dynamic function loading feature (also known as lazy loading). With dynamic function loading, loading the file doesn't fully read the function definitions in the file. Instead, each function definition contains a place-holder which refers to the file. The first time each function is called, it reads the full definition from the file, to replace the place-holder.
The advantage of dynamic function loading is that loading the file becomes much faster. This is a good thing for a file which contains many separate user-callable functions, if using one of them does not imply you will probably also use the rest. A specialized mode which provides many keyboard commands often has that usage pattern: a user may invoke the mode, but use only a few of the commands it provides.
The dynamic loading feature has certain disadvantages:
These problems will never happen in normal circumstances with installed Emacs files. But they are quite likely to happen with Lisp files that you are changing. The easiest way to prevent these problems is to reload the new compiled file immediately after each recompilation.
The byte compiler uses the dynamic function loading feature if the
variable byte-compile-dynamic is non-nil at compilation
time. Do not set this variable globally, since dynamic loading is
desirable only for certain files. Instead, enable the feature for
specific source files with file-local variable bindings. For example,
you could do it by writing this text in the source file's first line:
-*-byte-compile-dynamic: t;-*-
If this is non-
nil, the byte compiler generates compiled files that are set up for dynamic function loading.
If function is a byte-code function object, this immediately finishes loading the byte code of function from its byte-compiled file, if it is not fully loaded already. Otherwise, it does nothing. It always returns function.
These features permit you to write code to be evaluated during compilation of a program.
This form marks body to be evaluated both when you compile the containing code and when you run it (whether compiled or not).
You can get a similar result by putting body in a separate file and referring to that file with
require. That method is preferable when body is large. Effectivelyrequireis automaticallyeval-and-compile, the package is loaded both when compiling and executing.
autoloadis also effectivelyeval-and-compiletoo. It's recognized when compiling, so uses of such a function don't produce “not known to be defined” warnings.Most uses of
eval-and-compileare fairly sophisticated.If a macro has a helper function to build its result, and that macro is used both locally and outside the package, then
eval-and-compileshould be used to get the helper both when compiling and then later when running.If functions are defined programmatically (with
fsetsay), theneval-and-compilecan be used to have that done at compile-time as well as run-time, so calls to those functions are checked (and warnings about “not known to be defined” suppressed).
This form marks body to be evaluated at compile time but not when the compiled program is loaded. The result of evaluation by the compiler becomes a constant which appears in the compiled program. If you load the source file, rather than compiling it, body is evaluated normally.
If you have a constant that needs some calculation to produce,
eval-when-compilecan do that at compile-time. For example,(defvar my-regexp (eval-when-compile (regexp-opt '("aaa" "aba" "abb"))))If you're using another package, but only need macros from it (the byte compiler will expand those), then
eval-when-compilecan be used to load it for compiling, but not executing. For example,(eval-when-compile (require 'my-macro-package)) ;; only macros needed from thisThe same sort of thing goes for macros and
defsubstfunctions defined locally and only for use within the file. They are needed for compiling the file, but in most cases they are not needed for execution of the compiled file. For example,(eval-when-compile (unless (fboundp 'some-new-thing) (defmacro 'some-new-thing () (compatibility code))))This is often good for code that's only a fallback for compatibility with other versions of Emacs.
Common Lisp Note: At top level,
eval-when-compileis analogous to the Common Lisp idiom(eval-when (compile eval) ...). Elsewhere, the Common Lisp ‘#.’ reader macro (but not when interpreting) is closer to whateval-when-compiledoes.
Byte compilation outputs all errors and warnings into the buffer ‘*Compile-Log*’. The messages include file names and line numbers that identify the location of the problem. The usual Emacs commands for operating on compiler diagnostics work properly on these messages.
However, the warnings about functions that were used but not defined are always “located” at the end of the file, so these commands won't find the places they are really used. To do that, you must search for the function names.
You can suppress the compiler warning for calling an undefined
function func by conditionalizing the function call on an
fboundp test, like this:
(if (fboundp 'func) ...(func ...)...)
The call to func must be in the then-form of the
if, and func must appear quoted in the call to
fboundp. (This feature operates for cond as well.)
You can tell the compiler that a function is defined using
declare-function (see Declaring Functions). Likewise, you
can tell the compiler that a variable is defined using defvar
with no initial value.
You can suppress the compiler warning for a specific use of an
undefined variable variable by conditionalizing its use on a
boundp test, like this:
(if (boundp 'variable) ...variable...)
The reference to variable must be in the then-form of the
if, and variable must appear quoted in the call to
boundp.
You can suppress any and all compiler warnings within a certain
expression using the construct with-no-warnings:
In execution, this is equivalent to
(prognbody...), but the compiler does not issue warnings for anything that occurs inside body.We recommend that you use this construct around the smallest possible piece of code, to avoid missing possible warnings other than one one you intend to suppress.
More precise control of warnings is possible by setting the variable
byte-compile-warnings.
Byte-compiled functions have a special data type: they are byte-code function objects.
Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears as a function to be called. The printed representation for a byte-code function object is like that for a vector, with an additional ‘#’ before the opening ‘[’.
A byte-code function object must have at least four elements; there is no maximum number, but only the first six elements have any normal use. They are:
nil. The value may
be a number or a list, in case the documentation string is stored in a
file. Use the function documentation to get the real
documentation string (see Accessing Documentation).
nil for a function that isn't interactive.
Here's an example of a byte-code function object, in printed
representation. It is the definition of the command
backward-sexp.
#[(&optional arg)
"^H\204^F^@\301^P\302^H[!\207"
[arg 1 forward-sexp]
2
254435
"p"]
The primitive way to create a byte-code object is with
make-byte-code:
This function constructs and returns a byte-code function object with elements as its elements.
You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte compiler to create these objects; it makes the elements consistent (we hope).
You can access the elements of a byte-code object using aref;
you can also use vconcat to create a vector with the same
elements.
People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into human-readable form.
The byte-code interpreter is implemented as a simple stack machine. It pushes values onto a stack of its own, then pops them off to use them in calculations whose results are themselves pushed back on the stack. When a byte-code function returns, it pops a value off the stack and returns it as the value of the function.
In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables, by transferring values between variables and the stack.
This command displays the disassembled code for object. In interactive use, or if buffer-or-name is
nilor omitted, the output goes in a buffer named ‘*Disassemble*’. If buffer-or-name is non-nil, it must be a buffer or the name of an existing buffer. Then the output goes there, at point, and point is left before the output.The argument object can be a function name, a lambda expression or a byte-code object. If it is a lambda expression,
disassemblecompiles it and disassembles the resulting compiled code.
Here are two examples of using the disassemble function. We
have added explanatory comments to help you relate the byte-code to the
Lisp source; these do not appear in the output of disassemble.
(defun factorial (integer)
"Compute factorial of an integer."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
⇒ factorial
(factorial 4)
⇒ 24
(disassemble 'factorial)
-| byte-code for factorial:
doc: Compute factorial of an integer.
args: (integer)
0 varref integer ; Get the value of integer
; and push it onto the stack.
1 constant 1 ; Push 1 onto stack.
2 eqlsign ; Pop top two values off stack, compare
; them, and push result onto stack.
3 goto-if-nil 1 ; Pop and test top of stack;
; if nil, go to 1,
; else continue.
6 constant 1 ; Push 1 onto top of stack.
7 return ; Return the top element
; of the stack.
8:1 varref integer ; Push value of integer onto stack.
9 constant factorial ; Push factorial onto stack.
10 varref integer ; Push value of integer onto stack.
11 sub1 ; Pop integer, decrement value,
; push new value onto stack.
12 call 1 ; Call function factorial using
; the first (i.e., the top) element
; of the stack as the argument;
; push returned value onto stack.
13 mult ; Pop top two values off stack, multiply
; them, and push result onto stack.
14 return ; Return the top element of stack.
The silly-loop function is somewhat more complex:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
⇒ silly-loop
(disassemble 'silly-loop)
-| byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0 constant current-time-string ; Push
; current-time-string
; onto top of stack.
1 call 0 ; Call current-time-string
; with no argument,
; pushing result onto stack.
2 varbind t1 ; Pop stack and bind t1
; to popped value.
3:1 varref n ; Get value of n from
; the environment and push
; the value onto the stack.
4 sub1 ; Subtract 1 from top of stack.
5 dup ; Duplicate the top of the stack;
; i.e., copy the top of
; the stack and push the
; copy onto the stack.
6 varset n ; Pop the top of the stack,
; and bind n to the value.
; In effect, the sequence dup varset
; copies the top of the stack
; into the value of n
; without popping it.
7 constant 0 ; Push 0 onto stack.
8 gtr ; Pop top two values off stack,
; test if n is greater than 0
; and push result onto stack.
9 goto-if-not-nil 1 ; Goto 1 if n > 0
; (this continues the while loop)
; else continue.
12 varref t1 ; Push value of t1 onto stack.
13 constant current-time-string ; Push current-time-string
; onto top of stack.
14 call 0 ; Call current-time-string again.
15 unbind 1 ; Unbind t1 in local environment.
16 list2 ; Pop top two elements off stack,
; create a list of them,
; and push list onto stack.
17 return ; Return value of the top of stack.
The advice feature lets you add to the existing definition of a function, by advising the function. This is a cleaner method for a library to customize functions defined within Emacs—cleaner than redefining the whole function.
Each function can have multiple pieces of advice, separately defined. Each defined piece of advice can be enabled or disabled explicitly. All the enabled pieces of advice for any given function actually take effect when you activate advice for that function, or when you define or redefine the function. Note that enabling a piece of advice and activating advice for a function are not the same thing.
Usage Note: Advice is useful for altering the behavior of existing calls to an existing function. If you want the new behavior for new calls, or for key bindings, you should define a new function (or a new command) which uses the existing function.
Usage note: Advising a function can cause confusion in debugging, since people who debug calls to the original function may not notice that it has been modified with advice. Therefore, if you have the possibility to change the code of that function (or ask someone to do so) to run a hook, please solve the problem that way. Advice should be reserved for the cases where you cannot get the function changed.
In particular, this means that a file in Emacs should not put advice on a function in Emacs. There are currently a few exceptions to this convention, but we aim to correct them.
The command next-line moves point down vertically one or more
lines; it is the standard binding of C-n. When used on the last
line of the buffer, this command inserts a newline to create a line to
move to if next-line-add-newlines is non-nil (its default
is nil.)
Suppose you wanted to add a similar feature to previous-line,
which would insert a new line at the beginning of the buffer for the
command to move to (when next-line-add-newlines is
non-nil). How could you do this?
You could do it by redefining the whole function, but that is not modular. The advice feature provides a cleaner alternative: you can effectively add your code to the existing function definition, without actually changing or even seeing that definition. Here is how to do this:
(defadvice previous-line (before next-line-at-end
(&optional arg try-vscroll))
"Insert an empty line when moving up from the top line."
(if (and next-line-add-newlines (= arg 1)
(save-excursion (beginning-of-line) (bobp)))
(progn
(beginning-of-line)
(newline))))
This expression defines a piece of advice for the function
previous-line. This piece of advice is named
next-line-at-end, and the symbol before says that it is
before-advice which should run before the regular definition of
previous-line. (&optional arg try-vscroll) specifies
how the advice code can refer to the function's arguments.
When this piece of advice runs, it creates an additional line, in the situation where that is appropriate, but does not move point to that line. This is the correct way to write the advice, because the normal definition will run afterward and will move back to the newly inserted line.
Defining the advice doesn't immediately change the function
previous-line. That happens when you activate the advice,
like this:
(ad-activate 'previous-line)
This is what actually begins to use the advice that has been defined so
far for the function previous-line. Henceforth, whenever that
function is run, whether invoked by the user with C-p or
M-x, or called from Lisp, it runs the advice first, and its
regular definition second.
This example illustrates before-advice, which is one class of advice: it runs before the function's base definition. There are two other advice classes: after-advice, which runs after the base definition, and around-advice, which lets you specify an expression to wrap around the invocation of the base definition.
To define a piece of advice, use the macro defadvice. A call
to defadvice has the following syntax, which is based on the
syntax of defun and defmacro, but adds more:
(defadvice function (class name
[position] [arglist]
flags...)
[documentation-string]
[interactive-form]
body-forms...)
Here, function is the name of the function (or macro or special form) to be advised. From now on, we will write just “function” when describing the entity being advised, but this always includes macros and special forms.
In place of the argument list in an ordinary definition, an advice definition calls for several different pieces of information.
class specifies the class of the advice—one of before,
after, or around. Before-advice runs before the function
itself; after-advice runs after the function itself; around-advice is
wrapped around the execution of the function itself. After-advice and
around-advice can override the return value by setting
ad-return-value.
While advice is executing, after the function's original definition has been executed, this variable holds its return value, which will ultimately be returned to the caller after finishing all the advice. After-advice and around-advice can arrange to return some other value by storing it in this variable.
The argument name is the name of the advice, a non-nil
symbol. The advice name uniquely identifies one piece of advice, within all
the pieces of advice in a particular class for a particular
function. The name allows you to refer to the piece of
advice—to redefine it, or to enable or disable it.
The optional position specifies where, in the current list of
advice of the specified class, this new advice should be placed.
It should be either first, last or a number that specifies
a zero-based position (first is equivalent to 0). If no position
is specified, the default is first. Position values outside the
range of existing positions in this class are mapped to the beginning or
the end of the range, whichever is closer. The position value is
ignored when redefining an existing piece of advice.
The optional arglist can be used to define the argument list for the sake of advice. This becomes the argument list of the combined definition that is generated in order to run the advice (see Combined Definition). Therefore, the advice expressions can use the argument variables in this list to access argument values.
The argument list used in advice need not be the same as the argument list used in the original function, but must be compatible with it, so that it can handle the ways the function is actually called. If two pieces of advice for a function both specify an argument list, they must specify the same argument list.
See Argument Access in Advice, for more information about argument lists and advice, and a more flexible way for advice to access the arguments.
The remaining elements, flags, are symbols that specify further information about how to use this piece of advice. Here are the valid symbols and their meanings:
activateThis flag has no immediate effect if function itself is not defined yet (a
situation known as forward advice), because it is impossible to
activate an undefined function's advice. However, defining
function will automatically activate its advice.
protectunwind-protect form, so that it will execute even if the
previous code gets an error or uses throw. See Cleanups.
compileactivate is also specified.
See Combined Definition.
disablepreactivatedefadvice is
compiled or macroexpanded. This generates a compiled advised definition
according to the current advice state, which will be used during
activation if appropriate. See Preactivation.
This is useful only if this defadvice is byte-compiled.
The optional documentation-string serves to document this piece of
advice. When advice is active for function, the documentation for
function (as returned by documentation) combines the
documentation strings of all the advice for function with the
documentation string of its original function definition.
The optional interactive-form form can be supplied to change the interactive behavior of the original function. If more than one piece of advice has an interactive-form, then the first one (the one with the smallest position) found among all the advice takes precedence.
The possibly empty list of body-forms specifies the body of the advice. The body of an advice can access or change the arguments, the return value, the binding environment, and perform any other kind of side effect.
Warning: When you advise a macro, keep in mind that macros are expanded when a program is compiled, not when a compiled program is run. All subroutines used by the advice need to be available when the byte compiler expands the macro.
Around-advice lets you “wrap” a Lisp expression “around” the
original function definition. You specify where the original function
definition should go by means of the special symbol ad-do-it.
Where this symbol occurs inside the around-advice body, it is replaced
with a progn containing the forms of the surrounded code. Here
is an example:
(defadvice foo (around foo-around)
"Ignore case in `foo'."
(let ((case-fold-search t))
ad-do-it))
Its effect is to make sure that case is ignored in
searches when the original definition of foo is run.
This is not really a variable, rather a place-holder that looks like a variable. You use it in around-advice to specify the place to run the function's original definition and other “earlier” around-advice.
If the around-advice does not use ad-do-it, then it does not run
the original function definition. This provides a way to override the
original definition completely. (It also overrides lower-positioned
pieces of around-advice).
If the around-advice uses ad-do-it more than once, the original
definition is run at each place. In this way, around-advice can execute
the original definition (and lower-positioned pieces of around-advice)
several times. Another way to do that is by using ad-do-it
inside of a loop.
The macro defadvice resembles defun in that the code for
the advice, and all other information about it, are explicitly stated in
the source code. You can also create advice whose details are computed,
using the function ad-add-advice.
Calling
ad-add-adviceadds advice as a piece of advice to function in class class. The argument advice has this form:(name protected enabled definition)Here, protected and enabled are flags; if protected is non-
nil, the advice is protected against non-local exits (see Defining Advice), and if enabled isnilthe advice is initially disabled (see Enabling Advice). definition should have the form(advice . lambda)where lambda is a lambda expression; this lambda expression is called in order to perform the advice. See Lambda Expressions.
If the function argument to
ad-add-advicealready has one or more pieces of advice in the specified class, then position specifies where in the list to put the new piece of advice. The value of position can either befirst,last, or a number (counting from 0 at the beginning of the list). Numbers outside the range are mapped to the beginning or the end of the range, whichever is closer. The position value is ignored when redefining an existing piece of advice.If function already has a piece of advice with the same name, then the position argument is ignored and the old advice is replaced with the new one.
By default, advice does not take effect when you define it—only when
you activate advice for the function that was advised. However,
the advice will be activated automatically if you define or redefine
the function later. You can request the activation of advice for a
function when you define the advice, by specifying the activate
flag in the defadvice. But normally you activate the advice
for a function by calling the function ad-activate or one of
the other activation commands listed below.
Separating the activation of advice from the act of defining it permits you to add several pieces of advice to one function efficiently, without redefining the function over and over as each advice is added. More importantly, it permits defining advice for a function before that function is actually defined.
When a function's advice is first activated, the function's original definition is saved, and all enabled pieces of advice for that function are combined with the original definition to make a new definition. (Pieces of advice that are currently disabled are not used; see Enabling Advice.) This definition is installed, and optionally byte-compiled as well, depending on conditions described below.
In all of the commands to activate advice, if compile is
t (or anything but nil or a negative number), the
command also compiles the combined definition which implements the
advice. If it is nil or a negative number, what happens
depends on ad-default-compilation-action as described below.
This command activates all the advice defined for function.
Activating advice does nothing if function's advice is already active. But if there is new advice, added since the previous time you activated advice for function, it activates the new advice.
This command activates the advice for function if its advice is already activated. This is useful if you change the advice.
This command activates the advice for all functions whose advice is already activated. This is useful if you change the advice of some functions.
This command activates all pieces of advice whose names match regexp. More precisely, it activates all advice for any function which has at least one piece of advice that matches regexp.
This command deactivates all pieces of advice whose names match regexp. More precisely, it deactivates all advice for any function which has at least one piece of advice that matches regexp.
This command activates pieces of advice whose names match regexp, but only those for functions whose advice is already activated. Reactivating a function's advice is useful for putting into effect all the changes that have been made in its advice (including enabling and disabling specific pieces of advice; see Enabling Advice) since the last time it was activated.
Turn on automatic advice activation when a function is defined or redefined. This is the default mode.
Turn off automatic advice activation when a function is defined or redefined.
This variable controls whether to compile the combined definition that results from activating advice for a function.
A value of
alwaysspecifies to compile unconditionally. A value ofneverspecifies never compile the advice.A value of
maybespecifies to compile if the byte compiler is already loaded. A value oflike-originalspecifies to compile the advice if the original definition of the advised function is compiled or a built-in function.This variable takes effect only if the compile argument of
ad-activate(or any of the above functions) did not force compilation.
If the advised definition was constructed during “preactivation”
(see Preactivation), then that definition must already be compiled,
because it was constructed during byte-compilation of the file that
contained the defadvice with the preactivate flag.
Each piece of advice has a flag that says whether it is enabled or
not. By enabling or disabling a piece of advice, you can turn it on
and off without having to undefine and redefine it. For example, here is
how to disable a particular piece of advice named my-advice for
the function foo:
(ad-disable-advice 'foo 'before 'my-advice)
This function by itself only changes the enable flag for a piece of
advice. To make the change take effect in the advised definition, you
must activate the advice for foo again:
(ad-activate 'foo)
This command disables the piece of advice named name in class class on function.
This command enables the piece of advice named name in class class on function.
You can also disable many pieces of advice at once, for various functions, using a regular expression. As always, the changes take real effect only when you next reactivate advice for the functions in question.
This command disables all pieces of advice whose names match regexp, in all classes, on all functions.
This command enables all pieces of advice whose names match regexp, in all classes, on all functions.
Constructing a combined definition to execute advice is moderately expensive. When a library advises many functions, this can make loading the library slow. In that case, you can use preactivation to construct suitable combined definitions in advance.
To use preactivation, specify the preactivate flag when you
define the advice with defadvice. This defadvice call
creates a combined definition which embodies this piece of advice
(whether enabled or not) plus any other currently enabled advice for the
same function, and the function's own definition. If the
defadvice is compiled, that compiles the combined definition
also.
When the function's advice is subsequently activated, if the enabled advice for the function matches what was used to make this combined definition, then the existing combined definition is used, thus avoiding the need to construct one. Thus, preactivation never causes wrong results—but it may fail to do any good, if the enabled advice at the time of activation doesn't match what was used for preactivation.
Here are some symptoms that can indicate that a preactivation did not work properly, because of a mismatch.
byte-compile is included in the value of features even
though you did not ever explicitly use the byte compiler.
Compiled preactivated advice works properly even if the function itself is not defined until later; however, the function needs to be defined when you compile the preactivated advice.
There is no elegant way to find out why preactivated advice is not being
used. What you can do is to trace the function
ad-cache-id-verification-code (with the function
trace-function-background) before the advised function's advice
is activated. After activation, check the value returned by
ad-cache-id-verification-code for that function: verified
means that the preactivated advice was used, while other values give
some information about why they were considered inappropriate.
Warning: There is one known case that can make preactivation fail, in that a preconstructed combined definition is used even though it fails to match the current state of advice. This can happen when two packages define different pieces of advice with the same name, in the same class, for the same function. But you should avoid that anyway.
The simplest way to access the arguments of an advised function in the body of a piece of advice is to use the same names that the function definition uses. To do this, you need to know the names of the argument variables of the original function.
While this simple method is sufficient in many cases, it has a disadvantage: it is not robust, because it hard-codes the argument names into the advice. If the definition of the original function changes, the advice might break.
Another method is to specify an argument list in the advice itself. This avoids the need to know the original function definition's argument names, but it has a limitation: all the advice on any particular function must use the same argument list, because the argument list actually used for all the advice comes from the first piece of advice for that function.
A more robust method is to use macros that are translated into the proper access forms at activation time, i.e., when constructing the advised definition. Access macros access actual arguments by their (zero-based) position, regardless of how these actual arguments get distributed onto the argument variables of a function. This is robust because in Emacs Lisp the meaning of an argument is strictly determined by its position in the argument list.
This returns the list of actual arguments supplied starting at position.
This sets the list of actual arguments starting at position to value-list.
Now an example. Suppose the function foo is defined as
(defun foo (x y &optional z &rest r) ...)
and is then called with
(foo 0 1 2 3 4 5 6)
which means that x is 0, y is 1, z is 2 and r is
(3 4 5 6) within the body of foo. Here is what
ad-get-arg and ad-get-args return in this case:
(ad-get-arg 0) ⇒ 0
(ad-get-arg 1) ⇒ 1
(ad-get-arg 2) ⇒ 2
(ad-get-arg 3) ⇒ 3
(ad-get-args 2) ⇒ (2 3 4 5 6)
(ad-get-args 4) ⇒ (4 5 6)
Setting arguments also makes sense in this example:
(ad-set-arg 5 "five")
has the effect of changing the sixth argument to "five". If this
happens in advice executed before the body of foo is run, then
r will be (3 4 "five" 6) within that body.
Here is an example of setting a tail of the argument list:
(ad-set-args 0 '(5 4 3 2 1 0))
If this happens in advice executed before the body of foo is run,
then within that body, x will be 5, y will be 4, z
will be 3, and r will be (2 1 0) inside the body of
foo.
These argument constructs are not really implemented as Lisp macros. Instead they are implemented specially by the advice mechanism.
Advising a primitive function (see What Is a Function) is risky. Some primitive functions are used by the advice mechanism; advising them could cause an infinite recursion. Also, many primitive functions are called directly from C code. Calls to the primitive from Lisp code will take note of the advice, but calls from C code will ignore the advice.
When the advice facility constructs the combined definition, it needs
to know the argument list of the original function. This is not
always possible for primitive functions. When advice cannot determine
the argument list, it uses (&rest ad-subr-args), which always
works but is inefficient because it constructs a list of the argument
values. You can use ad-define-subr-args to declare the proper
argument names for a primitive function:
This function specifies that arglist should be used as the argument list for function function.
For example,
(ad-define-subr-args 'fset '(sym newdef))
specifies the argument list for the function fset.
Suppose that a function has n pieces of before-advice (numbered from 0 through n−1), m pieces of around-advice and k pieces of after-advice. Assuming no piece of advice is protected, the combined definition produced to implement the advice for a function looks like this:
(lambda arglist
[ [advised-docstring] [(interactive ...)] ]
(let (ad-return-value)
before-0-body-form...
....
before-n−1-body-form...
around-0-body-form...
around-1-body-form...
....
around-m−1-body-form...
(setq ad-return-value
apply original definition to arglist)
end-of-around-m−1-body-form...
....
end-of-around-1-body-form...
end-of-around-0-body-form...
after-0-body-form...
....
after-k−1-body-form...
ad-return-value))
Macros are redefined as macros, which means adding macro to
the beginning of the combined definition.
The interactive form is present if the original function or some piece
of advice specifies one. When an interactive primitive function is
advised, advice uses a special method: it calls the primitive with
call-interactively so that it will read its own arguments.
In this case, the advice cannot access the arguments.
The body forms of the various advice in each class are assembled according to their specified order. The forms of around-advice l are included in one of the forms of around-advice l − 1.
The innermost part of the around advice onion is
apply original definition to arglist
whose form depends on the type of the original function. The variable
ad-return-value is set to whatever this returns. The variable is
visible to all pieces of advice, which can access and modify it before
it is actually returned from the advised function.
The semantic structure of advised functions that contain protected
pieces of advice is the same. The only difference is that
unwind-protect forms ensure that the protected advice gets
executed even if some previous piece of advice had an error or a
non-local exit. If any around-advice is protected, then the whole
around-advice onion is protected as a result.
There are three ways to investigate a problem in an Emacs Lisp program, depending on what you are doing with the program when the problem appears.
Another useful debugging tool is the dribble file. When a dribble file is open, Emacs copies all keyboard input characters to that file. Afterward, you can examine the file to find out what input was used. See Terminal Input.
For debugging problems in terminal descriptions, the
open-termscript function can be useful. See Terminal Output.
The ordinary Lisp debugger provides the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See Recursive Editing.
The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error.
However, entry to the debugger is not a normal consequence of an
error. Many commands frequently cause Lisp errors when invoked
inappropriately, and during ordinary editing it would be very
inconvenient to enter the debugger each time this happens. So if you
want errors to enter the debugger, set the variable
debug-on-error to non-nil. (The command
toggle-debug-on-error provides an easy way to do this.)
This variable determines whether the debugger is called when an error is signaled and not handled. If
debug-on-errorist, all kinds of errors call the debugger, except those listed indebug-ignored-errors(see below). If it isnil, none call the debugger. (Note thateval-expression-debug-on-erroraffects the setting of this variable in some cases; see below.)The value can also be a list of error conditions that should call the debugger. For example, if you set it to the list
(void-variable), then only errors about a variable that has no value invoke the debugger.When this variable is non-
nil, Emacs does not create an error handler around process filter functions and sentinels. Therefore, errors in these functions also invoke the debugger. See Processes.
This variable specifies certain kinds of errors that should not enter the debugger. Its value is a list of error condition symbols and/or regular expressions. If the error has any of those condition symbols, or if the error message matches any of the regular expressions, then that error does not enter the debugger, regardless of the value of
debug-on-error.The normal value of this variable lists several errors that happen often during editing but rarely result from bugs in Lisp programs. However, “rarely” is not “never”; if your program fails with an error that matches this list, you will need to change this list in order to debug the error. The easiest way is usually to set
debug-ignored-errorstonil.
If this variable has a non-
nilvalue, thendebug-on-erroris set totwhen evaluating with the commandeval-expression. Ifeval-expression-debug-on-errorisnil, then the value ofdebug-on-erroris not changed. See Evaluating Emacs-Lisp Expressions.
Normally, errors that are caught by
condition-casenever run the debugger, even ifdebug-on-erroris non-nil. In other words,condition-casegets a chance to handle the error before the debugger gets a chance.If you set
debug-on-signalto a non-nilvalue, then the debugger gets the first chance at every error; an error will invoke the debugger regardless of anycondition-case, if it fits the criteria specified by the values ofdebug-on-erroranddebug-ignored-errors.Warning: This variable is strong medicine! Various parts of Emacs handle errors in the normal course of affairs, and you may not even realize that errors happen there. If you set
debug-on-signalto a non-nilvalue, those errors will enter the debugger.Warning:
debug-on-signalhas no effect whendebug-on-errorisnil.
To debug an error that happens during loading of the init
file, use the option ‘--debug-init’. This binds
debug-on-error to t while loading the init file, and
bypasses the condition-case which normally catches errors in the
init file.
When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes a quit.
Ordinary quitting gives no information about why the program was
looping. To get more information, you can set the variable
debug-on-quit to non-nil. Quitting with C-g is not
considered an error, and debug-on-error has no effect on the
handling of C-g. Likewise, debug-on-quit has no effect on
errors.
Once you have the debugger running in the middle of the infinite loop, you can proceed from the debugger using the stepping commands. If you step through the entire loop, you will probably get enough information to solve the problem.
This variable determines whether the debugger is called when
quitis signaled and not handled. Ifdebug-on-quitis non-nil, then the debugger is called whenever you quit (that is, type C-g). Ifdebug-on-quitisnil, then the debugger is not called when you quit. See Quitting.
To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.
This function requests function-name to invoke the debugger each time it is called. It works by inserting the form
(implement-debug-on-entry)into the function definition as the first form.Any function or macro defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. If the function is a command, it will enter the debugger when called from Lisp and when called interactively (after the reading of the arguments). You can also set debug-on-entry for primitive functions (i.e., those written in C) this way, but it only takes effect when the primitive is called from Lisp code. Debug-on-entry is not allowed for special forms.
When
debug-on-entryis called interactively, it prompts for function-name in the minibuffer. If the function is already set up to invoke the debugger on entry,debug-on-entrydoes nothing.debug-on-entryalways returns function-name.Warning: if you redefine a function after using
debug-on-entryon it, the code to enter the debugger is discarded by the redefinition. In effect, redefining the function cancels the break-on-entry feature for that function.Here's an example to illustrate use of this function:
(defun fact (n) (if (zerop n) 1 (* n (fact (1- n))))) ⇒ fact (debug-on-entry 'fact) ⇒ fact (fact 3) ------ Buffer: *Backtrace* ------ Debugger entered--entering a function: * fact(3) eval((fact 3)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ------ Buffer: *Backtrace* ------ (symbol-function 'fact) ⇒ (lambda (n) (debug (quote debug)) (if (zerop n) 1 (* n (fact (1- n)))))
This function undoes the effect of
debug-on-entryon function-name. When called interactively, it prompts for function-name in the minibuffer. If function-name is omitted ornil, it cancels break-on-entry for all functions. Callingcancel-debug-on-entrydoes nothing to a function which is not currently set up to break on entry.
You can cause the debugger to be called at a certain point in your
program by writing the expression (debug) at that point. To do
this, visit the source file, insert the text ‘(debug)’ at the
proper place, and type C-M-x (eval-defun, a Lisp mode key
binding). Warning: if you do this for temporary debugging
purposes, be sure to undo this insertion before you save the file!
The place where you insert ‘(debug)’ must be a place where an
additional form can be evaluated and its value ignored. (If the value
of (debug) isn't ignored, it will alter the execution of the
program!) The most common suitable places are inside a progn or
an implicit progn (see Sequencing).
When the debugger is entered, it displays the previously selected buffer in one window and a buffer named ‘*Backtrace*’ in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error).
The backtrace buffer is read-only and uses a special major mode, Debugger mode, in which letters are defined as debugger commands. The usual Emacs editing commands are available; thus, you can switch windows to examine the buffer that was being edited at the time of the error, switch buffers, visit files, or do any other sort of editing. However, the debugger is a recursive editing level (see Recursive Editing) and it is wise to go back to the backtrace buffer and exit the debugger (with the q command) when you are finished with it. Exiting the debugger gets out of the recursive edit and kills the backtrace buffer.
The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the current frame. Some of the debugger commands operate on the current frame. If a line starts with a star, that means that exiting that frame will call the debugger again. This is useful for examining the return value of a function.
If a function name is underlined, that means the debugger knows where its source code is located. You can click Mouse-2 on that name, or move to it and type <RET>, to visit the source code.
The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.
The debugger buffer (in Debugger mode) provides special commands in addition to the usual Emacs commands. The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source for the function and type C-M-x on its definition.) You cannot use the Lisp debugger to step through a primitive function.
Here is a list of Debugger mode commands:
Continuing is possible after entry to the debugger due to function entry
or exit, explicit invocation, or quitting. You cannot continue if the
debugger was entered because of an error.
The stack frame made for the function call which enters the debugger in
this way will be flagged automatically so that the debugger will be
called again when the frame is exited. You can use the u command
to cancel this flag.
debug-on-entry.
If the debugger was entered due to a C-g but you really want
to quit, and not debug, use the q command.
The r command is useful when the debugger was invoked due to exit
from a Lisp call frame (as requested with b or by entering the
frame with d); then the value specified in the r command is
used as the value of that frame. It is also useful if you call
debug and use its return value. Otherwise, r has the same
effect as c, and the specified return value does not matter.
You can't use r when the debugger was entered due to an error.
debug-on-entry. Warning: if you redefine such a
function and thus cancel the effect of debug-on-entry, it may
erroneously show up in this list.
Here we describe in full detail the function debug that is used
to invoke the debugger.
This function enters the debugger. It switches buffers to a buffer named ‘*Backtrace*’ (or ‘*Backtrace*<2>’ if it is the second recursive entry to the debugger, etc.), and fills it with information about the stack of Lisp function calls. It then enters a recursive edit, showing the backtrace buffer in Debugger mode.
The Debugger mode c, d, j, and r commands exit the recursive edit; then
debugswitches back to the previous buffer and returns to whatever calleddebug. This is the only way the functiondebugcan return to its caller.The use of the debugger-args is that
debugdisplays the rest of its arguments at the top of the ‘*Backtrace*’ buffer, so that the user can see them. Except as described below, this is the only way these arguments are used.However, certain values for first argument to
debughave a special significance. (Normally, these values are used only by the internals of Emacs, and not by programmers callingdebug.) Here is a table of these special values:
lambda- A first argument of
lambdameansdebugwas called because of entry to a function whendebug-on-next-callwas non-nil. The debugger displays ‘Debugger entered--entering a function:’ as a line of text at the top of the buffer.debugdebugas first argument meansdebugwas called because of entry to a function that was set to debug on entry. The debugger displays the string ‘Debugger entered--entering a function:’, just as in thelambdacase. It also marks the stack frame for that function so that it will invoke the debugger when exited.t- When the first argument is
t, this indicates a call todebugdue to evaluation of a function call form whendebug-on-next-callis non-nil. The debugger displays ‘Debugger entered--beginning evaluation of function call form:’ as the top line in the buffer.exit- When the first argument is
exit, it indicates the exit of a stack frame previously marked to invoke the debugger on exit. The second argument given todebugin this case is the value being returned from the frame. The debugger displays ‘Debugger entered--returning value:’ in the top line of the buffer, followed by the value being returned.error- When the first argument is
error, the debugger indicates that it is being entered because an error orquitwas signaled and not handled, by displaying ‘Debugger entered--Lisp error:’ followed by the error signaled and any arguments tosignal. For example,(let ((debug-on-error t)) (/ 1 0)) ------ Buffer: *Backtrace* ------ Debugger entered--Lisp error: (arith-error) /(1 0) ... ------ Buffer: *Backtrace* ------If an error was signaled, presumably the variable
debug-on-erroris non-nil. Ifquitwas signaled, then presumably the variabledebug-on-quitis non-nil.nil- Use
nilas the first of the debugger-args when you want to enter the debugger explicitly. The rest of the debugger-args are printed on the top line of the buffer. You can use this feature to display messages—for example, to remind yourself of the conditions under whichdebugis called.
This section describes functions and variables used internally by the debugger.
The value of this variable is the function to call to invoke the debugger. Its value must be a function of any number of arguments, or, more typically, the name of a function. This function should invoke some kind of debugger. The default value of the variable is
debug.The first argument that Lisp hands to the function indicates why it was called. The convention for arguments is detailed in the description of
debug(see Invoking the Debugger).
This function prints a trace of Lisp function calls currently active. This is the function used by
debugto fill up the ‘*Backtrace*’ buffer. It is written in C, since it must have access to the stack to determine which function calls are active. The return value is alwaysnil.In the following example, a Lisp expression calls
backtraceexplicitly. This prints the backtrace to the streamstandard-output, which, in this case, is the buffer ‘backtrace-output’.Each line of the backtrace represents one function call. The line shows the values of the function's arguments if they are all known; if they are still being computed, the line says so. The arguments of special forms are elided.
(with-output-to-temp-buffer "backtrace-output" (let ((var 1)) (save-excursion (setq var (eval '(progn (1+ var) (list 'testing (backtrace)))))))) ⇒ (testing nil) ----------- Buffer: backtrace-output ------------ backtrace() (list ...computing arguments...) (progn ...) eval((progn (1+ var) (list (quote testing) (backtrace)))) (setq ...) (save-excursion ...) (let ...) (with-output-to-temp-buffer ...) eval((with-output-to-temp-buffer ...)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ----------- Buffer: backtrace-output ------------
If this variable is non-
nil, it says to call the debugger before the nexteval,applyorfuncall. Entering the debugger setsdebug-on-next-calltonil.The d command in the debugger works by setting this variable.
This function sets the debug-on-exit flag of the stack frame level levels down the stack, giving it the value flag. If flag is non-
nil, this will cause the debugger to be entered when that frame later exits. Even a nonlocal exit through that frame will enter the debugger.This function is used only by the debugger.
This variable records the debugging status of the current interactive command. Each time a command is called interactively, this variable is bound to
nil. The debugger can set this variable to leave information for future debugger invocations during the same command invocation.The advantage of using this variable rather than an ordinary global variable is that the data will never carry over to a subsequent command invocation.
The function
backtrace-frameis intended for use in Lisp debuggers. It returns information about what computation is happening in the stack frame frame-number levels down.If that frame has not evaluated the arguments yet, or is a special form, the value is
(nilfunction arg-forms...).If that frame has evaluated its arguments and called its function already, the return value is
(tfunction arg-values...).In the return value, function is whatever was supplied as the car of the evaluated list, or a
lambdaexpression in the case of a macro call. If the function has a&restargument, that is represented as the tail of the list arg-values.If frame-number is out of range,
backtrace-framereturnsnil.
Edebug is a source-level debugger for Emacs Lisp programs, with which you can:
The first three sections below should tell you enough about Edebug to start using it.
To debug a Lisp program with Edebug, you must first instrument
the Lisp code that you want to debug. A simple way to do this is to
first move point into the definition of a function or macro and then do
C-u C-M-x (eval-defun with a prefix argument). See
Instrumenting, for alternative ways to instrument code.
Once a function is instrumented, any call to the function activates Edebug. Depending on which Edebug execution mode you have selected, activating Edebug may stop execution and let you step through the function, or it may update the display and continue execution while checking for debugging commands. The default execution mode is step, which stops execution. See Edebug Execution Modes.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the source code buffer, and it is temporarily read-only.
An arrow in the left fringe indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.
If you instrument the definition of fac (shown below) and then
execute (fac 3), here is what you would normally see. Point is
at the open-parenthesis before if.
(defun fac (n)
=>-!-(if (< 0 n)
(* n (fac (1- n)))
1))
The places within a function where Edebug can stop execution are called
stop points. These occur both before and after each subexpression
that is a list, and also after each variable reference.
Here we use periods to show the stop points in the function
fac:
(defun fac (n)
.(if .(< 0 n.).
.(* n. .(fac .(1- n.).).).
1).)
The special commands of Edebug are available in the source code buffer
in addition to the commands of Emacs Lisp mode. For example, you can
type the Edebug command <SPC> to execute until the next stop point.
If you type <SPC> once after entry to fac, here is the
display you will see:
(defun fac (n)
=>(if -!-(< 0 n)
(* n (fac (1- n)))
1))
When Edebug stops execution after an expression, it displays the expression's value in the echo area.
Other frequently used commands are b to set a breakpoint at a stop point, g to execute until a breakpoint is reached, and q to exit Edebug and return to the top-level command loop. Type ? to display a list of all Edebug commands.
In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places.
When you invoke command C-M-x (eval-defun) with a
prefix argument on a function definition, it instruments the
definition before evaluating it. (This does not modify the source
code itself.) If the variable edebug-all-defs is
non-nil, that inverts the meaning of the prefix argument: in
this case, C-M-x instruments the definition unless it has
a prefix argument. The default value of edebug-all-defs is
nil. The command M-x edebug-all-defs toggles the value
of the variable edebug-all-defs.
If edebug-all-defs is non-nil, then the commands
eval-region, eval-current-buffer, and eval-buffer
also instrument any definitions they evaluate. Similarly,
edebug-all-forms controls whether eval-region should
instrument any form, even non-defining forms. This doesn't apply
to loading or evaluations in the minibuffer. The command M-x
edebug-all-forms toggles this option.
Another command, M-x edebug-eval-top-level-form, is available to
instrument any top-level form regardless of the values of
edebug-all-defs and edebug-all-forms.
While Edebug is active, the command I
(edebug-instrument-callee) instruments the definition of the
function or macro called by the list form after point, if it is not already
instrumented. This is possible only if Edebug knows where to find the
source for that function; for this reason, after loading Edebug,
eval-region records the position of every definition it
evaluates, even if not instrumenting it. See also the i command
(see Jumping), which steps into the call after instrumenting the
function.
Edebug knows how to instrument all the standard special forms,
interactive forms with an expression argument, anonymous lambda
expressions, and other defining forms. However, Edebug cannot determine
on its own what a user-defined macro will do with the arguments of a
macro call, so you must provide that information using Edebug
specifications; for details, see Edebug and Macros.
When Edebug is about to instrument code for the first time in a
session, it runs the hook edebug-setup-hook, then sets it to
nil. You can use this to load Edebug specifications
associated with a package you are using, but only when you use Edebug.
To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument. There are two ways of
evaluating forms that never instrument them: from a file with
load, and from the minibuffer with eval-expression
(M-:).
If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an invalid-read-syntax error.
See Edebug Eval, for other evaluation functions available inside of Edebug.
Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major or minor modes. The current Edebug execution mode determines how far Edebug continues execution before stopping—whether it stops at each stop point, or continues to the next breakpoint, for example—and how much Edebug displays the progress of the evaluation before it stops.
Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands; all except for S resume execution of the program, at least for a certain distance.
edebug-stop).
edebug-step-mode).
edebug-next-mode). Also see edebug-forward-sexp in
Jumping.
edebug-trace-mode).
edebug-Trace-fast-mode).
edebug-go-mode). See Breakpoints.
edebug-continue-mode).
edebug-Continue-fast-mode).
edebug-Go-nonstop-mode). You
can still stop the program by typing S, or any editing command.
In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list.
While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command you typed. For example, typing t during execution switches to trace mode at the next stop point. You can use S to stop execution without doing anything else.
If your function happens to read input, a character you type intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.
Keyboard macros containing the commands in this section do not
completely work: exiting from Edebug, to resume the program, loses track
of the keyboard macro. This is not easy to fix. Also, defining or
executing a keyboard macro outside of Edebug does not affect commands
inside Edebug. This is usually an advantage. See also the
edebug-continue-kbd-macro option in Edebug Options.
When you enter a new Edebug level, the initial execution mode comes
from the value of the variable edebug-initial-mode
(see Edebug Options). By default, this specifies step mode. Note
that you may reenter the same Edebug level several times if, for
example, an instrumented function is called several times from one
command.
This option specifies how many seconds to wait between execution steps in trace mode or continue mode. The default is 1 second.
The commands described in this section execute until they reach a specified location. All except i make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. See Breakpoints, for the details on breakpoints.
These commands may fail to work as expected in case of nonlocal exit, as that can bypass the temporary breakpoint where you expected the program to stop.
edebug-goto-here).
edebug-forward-sexp).
edebug-step-out).
The h command proceeds to the stop point at or after the current location of point, using a temporary breakpoint.
The f command runs the program forward over one expression. More
precisely, it sets a temporary breakpoint at the position that
forward-sexp would reach, then executes in go mode so that
the program will stop at breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
You must check that the position forward-sexp finds is a place
that the program will really get to. In cond, for example,
this may not be true.
For flexibility, the f command does forward-sexp starting
at point, rather than at the stop point. If you want to execute one
expression from the current stop point, first type w
(edebug-where) to move point there, and then type f.
The o command continues “out of” an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, o continues until just before the last sexp in the definition. If that is where you are now, it returns from the function and then stops. In other words, this command does not exit the currently executing function unless you are positioned after the last sexp.
The i command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late.
The i command instruments the function or macro it's supposed to step into, if it isn't instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it.
Some miscellaneous Edebug commands are described here.
edebug-help).
abort-recursive-edit).
top-level). This
exits all recursive editing levels, including all levels of Edebug
activity. However, instrumented code protected with
unwind-protect or condition-case forms may resume
debugging.
edebug-top-level-nonstop).
edebug-previous-result).
edebug-backtrace).
You cannot use debugger commands in the backtrace buffer in Edebug as you would in the standard debugger.
The backtrace buffer is killed automatically when you continue execution.
You can invoke commands from Edebug that activate Edebug again recursively. Whenever Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the pending evaluations with d.
Edebug's step mode stops execution when the next stop point is reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source breakpoints.
While using Edebug, you can specify breakpoints in the program you are testing: these are places where execution should stop. You can set a breakpoint at any stop point, as defined in Using Edebug. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints:
edebug-set-breakpoint). If you use a prefix argument, the
breakpoint is temporary—it turns off the first time it stops the
program.
edebug-unset-breakpoint).
nil value
(edebug-set-conditional-breakpoint). With a prefix argument,
the breakpoint is temporary.
edebug-next-breakpoint).
While in Edebug, you can set a breakpoint with b and unset one with u. First move point to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect.
Re-evaluating or reinstrumenting a definition removes all of its previous breakpoints.
A conditional breakpoint tests a condition each time the program
gets there. Any errors that occur as a result of evaluating the
condition are ignored, as if the result were nil. To set a
conditional breakpoint, use x, and specify the condition
expression in the minibuffer. Setting a conditional breakpoint at a
stop point that has a previously established conditional breakpoint puts
the previous condition expression in the minibuffer so you can edit it.
You can make a conditional or unconditional breakpoint temporary by using a prefix argument with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset.
Edebug always stops or pauses at a breakpoint, except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B command, which moves point to the next breakpoint following point, within the same function, or to the first breakpoint if there are no following breakpoints. This command does not continue execution—it just moves point in the buffer.
A global break condition stops execution when a specified
condition is satisfied, no matter where that may occur. Edebug
evaluates the global break condition at every stop point; if it
evaluates to a non-nil value, then execution stops or pauses
depending on the execution mode, as if a breakpoint had been hit. If
evaluating the condition gets an error, execution does not stop.
The condition expression is stored in
edebug-global-break-condition. You can specify a new expression
using the X command from the source code buffer while Edebug is
active, or using C-x X X from any buffer at any time, as long as
Edebug is loaded (edebug-set-global-break-condition).
The global break condition is the simplest way to find where in your
code some event occurs, but it makes code run much more slowly. So you
should reset the condition to nil when not using it.
All breakpoints in a definition are forgotten each time you
reinstrument it. If you wish to make a breakpoint that won't be
forgotten, you can write a source breakpoint, which is simply a
call to the function edebug in your source code. You can, of
course, make such a call conditional. For example, in the fac
function, you can insert the first line as shown below, to stop when the
argument reaches zero:
(defun fac (n)
(if (= n 0) (edebug))
(if (< 0 n)
(* n (fac (1- n)))
1))
When the fac definition is instrumented and the function is
called, the call to edebug acts as a breakpoint. Depending on
the execution mode, Edebug stops or pauses there.
If no instrumented code is being executed when edebug is called,
that function calls debug.
Emacs normally displays an error message when an error is signaled and
not handled with condition-case. While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors. You can customize this with the options edebug-on-error
and edebug-on-quit; see Edebug Options.
When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, and within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case, you might want to display a full backtrace (see Edebug Misc).
If you change debug-on-error or debug-on-quit while
Edebug is active, these changes will be forgotten when Edebug becomes
inactive. Furthermore, during Edebug's recursive edit, these variables
are bound to the values they had outside of Edebug.
These Edebug commands let you view aspects of the buffer and window status as they were before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug.
edebug-view-outside). Type C-x X w to return to Edebug.
edebug-bounce-point), pausing for one second
before returning to Edebug. With a prefix argument n, pause for
n seconds instead.
edebug-where).
If you use this command in a different window displaying the same
buffer, that window will be used instead to display the current
definition in the future.
edebug-toggle-save-windows).
With a prefix argument, W only toggles saving and restoring of
the selected window. To specify a window that is not displaying the
source code buffer, you must use C-x X W from the global keymap.
You can view the outside window configuration with v or just bounce to the point in the current buffer with p, even if it is not normally displayed.
After moving point, you may wish to jump back to the stop point. You can do that with w from a source code buffer. You can jump back to the stop point in the source code buffer from any buffer using C-x X w.
Each time you use W to turn saving off, Edebug forgets the saved outside window configuration—so that even if you turn saving back on, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). However, the automatic redisplay of ‘*edebug*’ and ‘*edebug-trace*’ may conflict with the buffers you wish to see unless you have enough windows open.
While within Edebug, you can evaluate expressions “as if” Edebug were not running. Edebug tries to be invisible to the expression's evaluation and printing. Evaluation of expressions that cause side effects will work as expected, except for changes to data that Edebug explicitly saves and restores. See The Outside Context, for details on this process.
edebug-eval-expression). That is, Edebug tries to minimize its
interference with the evaluation.
eval-expression).
edebug-eval-last-sexp).
Edebug supports evaluation of expressions containing references to
lexically bound symbols created by the following constructs in
cl.el: lexical-let, macrolet, and
symbol-macrolet.
You can use the evaluation list buffer, called ‘*edebug*’, to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display.
edebug-visit-eval-list).
In the ‘*edebug*’ buffer you can use the commands of Lisp Interaction mode (see Lisp Interaction) as well as these special commands:
edebug-eval-print-last-sexp).
edebug-eval-last-sexp).
edebug-update-eval-list).
edebug-delete-eval-item).
edebug-where).
You can evaluate expressions in the evaluation list window with C-j or C-x C-e, just as you would in ‘*scratch*’; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost when you continue execution; but you can set up an evaluation list consisting of expressions to be evaluated each time execution stops.
To do this, write one or more evaluation list groups in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines.
The command C-c C-u (edebug-update-eval-list) rebuilds the
evaluation list, scanning the buffer and using the first expression of
each group. (The idea is that the second expression of the group is the
value previously computed and displayed.)
Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type C-c C-u again without changing the buffer text, the evaluation list is effectively unchanged.
If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions using variables that are not currently valid do not interrupt your debugging.
Here is an example of what the evaluation list window looks like after several expressions have been added to it:
(current-buffer)
#<buffer *scratch*>
;---------------------------------------------------------------
(selected-window)
#<window 16 on *scratch*>
;---------------------------------------------------------------
(point)
196
;---------------------------------------------------------------
bad-var
"Symbol's value as variable is void: bad-var"
;---------------------------------------------------------------
(recursion-depth)
0
;---------------------------------------------------------------
this-command
eval-last-sexp
;---------------------------------------------------------------
To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. To add a new expression to the evaluation list, insert the expression at a suitable place, insert a new comment line, then type C-c C-u. You need not insert dashes in the comment line—its contents don't matter.
After selecting ‘*edebug*’, you can return to the source code buffer with C-c C-w. The ‘*edebug*’ buffer is killed when you continue execution, and recreated next time it is needed.
If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it.
One way to cope with circular structure is to set print-length
or print-level to truncate the printing. Edebug does this for
you; it binds print-length and print-level to the values
of the variables edebug-print-length and
edebug-print-level (so long as they have non-nil
values). See Output Variables.
If non-
nil, Edebug bindsprint-lengthto this value while printing results. The default value is50.
If non-
nil, Edebug bindsprint-levelto this value while printing results. The default value is50.
You can also print circular structures and structures that share
elements more informatively by binding print-circle
to a non-nil value.
Here is an example of code that creates a circular structure:
(setq a '(x y))
(setcar a a)
Custom printing prints this as ‘Result: #1=(#1# y)’. The ‘#1=’ notation labels the structure that follows it with the label ‘1’, and the ‘#1#’ notation references the previously labeled structure. This notation is used for any shared elements of lists or vectors.
If non-
nil, Edebug bindsprint-circleto this value while printing results. The default value ist.
Other programs can also use custom printing; see cust-print.el for details.
Edebug can record an execution trace, storing it in a buffer named
‘*edebug-trace*’. This is a log of function calls and returns,
showing the function names and their arguments and values. To enable
trace recording, set edebug-trace to a non-nil value.
Making a trace buffer is not the same thing as using trace execution mode (see Edebug Execution Modes).
When trace recording is enabled, each function entry and exit adds lines to the trace buffer. A function entry record consists of ‘::::{’, followed by the function name and argument values. A function exit record consists of ‘::::}’, followed by the function name and result of the function.
The number of ‘:’s in an entry shows its recursion depth. You can use the braces in the trace buffer to find the matching beginning or end of function calls.
You can customize trace recording for function entry and exit by
redefining the functions edebug-print-trace-before and
edebug-print-trace-after.
This macro requests additional trace information around the execution of the body forms. The argument string specifies text to put in the trace buffer, after the ‘{’ or ‘}’. All the arguments are evaluated, and
edebug-tracingreturns the value of the last form in body.
This function inserts text in the trace buffer. It computes the text with
(apply 'formatformat-string format-args). It also appends a newline to separate entries.
edebug-tracing and edebug-trace insert lines in the
trace buffer whenever they are called, even if Edebug is not active.
Adding text to the trace buffer also scrolls its window to show the last
lines inserted.
Edebug provides rudimentary coverage testing and display of execution frequency.
Coverage testing works by comparing the result of each expression with the previous result; each form in the program is considered “covered” if it has returned two different values since you began testing coverage in the current Emacs session. Thus, to do coverage testing on your program, execute it under various conditions and note whether it behaves correctly; Edebug will tell you when you have tried enough different conditions that each form has returned two different values.
Coverage testing makes execution slower, so it is only done if
edebug-test-coverage is non-nil. Frequency counting is
performed for all executions of an instrumented function, even if the
execution mode is Go-nonstop, and regardless of whether coverage testing
is enabled.
Use C-x X = (edebug-display-freq-count) to display both
the coverage information and the frequency counts for a definition.
Just = (edebug-temp-display-freq-count) displays the same
information temporarily, only until you type another key.
This command displays the frequency count data for each line of the current definition.
It inserts frequency counts as comment lines after each line of code. You can undo all insertions with one
undocommand. The counts appear under the ‘(’ before an expression or the ‘)’ after an expression, or on the last character of a variable. To simplify the display, a count is not shown if it is equal to the count of an earlier expression on the same line.The character ‘=’ following the count for an expression says that the expression has returned the same value each time it was evaluated. In other words, it is not yet “covered” for coverage testing purposes.
To clear the frequency count and coverage data for a definition, simply reinstrument it with
eval-defun.
For example, after evaluating (fac 5) with a source
breakpoint, and setting edebug-test-coverage to t, when
the breakpoint is reached, the frequency data looks like this:
(defun fac (n)
(if (= n 0) (edebug))
;#6 1 = =5
(if (< 0 n)
;#5 =
(* n (fac (1- n)))
;# 5 0
1))
;# 0
The comment lines show that fac was called 6 times. The
first if statement returned 5 times with the same result each
time; the same is true of the condition on the second if.
The recursive call of fac did not return at all.
Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. Edebug also tries to be transparent when you evaluate expressions with e or with the evaluation list buffer, by temporarily restoring the outside context. This section explains precisely what context Edebug restores, and how Edebug fails to be completely transparent.
Whenever Edebug is entered, it needs to save and restore certain data before even deciding whether to make trace information or stop the program.
max-lisp-eval-depth and max-specpdl-size are both
increased to reduce Edebug's impact on the stack. You could, however,
still run out of stack space when using Edebug.
executing-kbd-macro is bound to nil
unless edebug-continue-kbd-macro is non-nil.
When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from “outside” Edebug (see Window Configurations). When you exit Edebug (by continuing the program), it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue execution, the program re-enters Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the “outside” configuration. Consequently, what you see is the same window configuration as the last time Edebug was active, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data (though some of them are deliberately not restored if an error or quit signal occurs).
edebug-save-windows is non-nil (see Edebug Options).
The window configuration is not restored on error or quit, but the
outside selected window is reselected even on error or quit in
case a save-excursion is active. If the value of
edebug-save-windows is a list, only the listed windows are saved
and restored.
The window start and horizontal scrolling of the source code buffer are not restored, however, so that the display remains coherent within Edebug.
edebug-save-displayed-buffer-points is non-nil.
overlay-arrow-position and
overlay-arrow-string are saved and restored, so you can safely
invoke Edebug from the recursive edit elsewhere in the same buffer.
cursor-in-echo-area is locally bound to nil so that
the cursor shows up in the window.
When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:
last-command, this-command,
last-input-event, last-command-event,
last-event-frame, last-nonmenu-event, and
track-mouse. Commands used within Edebug do not affect these
variables outside of Edebug.
Executing commands within Edebug can change the key sequence that
would be returned by this-command-keys, and there is no way to
reset the key sequence from Lisp.
Edebug cannot save and restore the value of
unread-command-events. Entering Edebug while this variable has a
nontrivial value can interfere with execution of the program you are
debugging.
command-history. In rare cases this can alter execution.
standard-output and standard-input are bound to nil
by the recursive-edit, but Edebug temporarily restores them during
evaluations.
defining-kbd-macro is bound to
edebug-continue-kbd-macro.
To make Edebug properly instrument expressions that call macros, some extra care is needed. This subsection explains the details.
When Edebug instruments an expression that calls a Lisp macro, it needs additional information about the macro to do the job properly. This is because there is no a-priori way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation may occur explicitly in the macro body, or when the resulting expansion is evaluated, or any time later.)
Therefore, you must define an Edebug specification for each macro
that Edebug will encounter, to explain the format of calls to that
macro. To do this, add a debug declaration to the macro
definition. Here is a simple example that shows the specification for
the for example macro (see Argument Evaluation).
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(declare (debug (symbolp "from" form "to" form "do" &rest form)))
...)
The Edebug specification says which parts of a call to the macro are
forms to be evaluated. For simple macros, the specification
often looks very similar to the formal argument list of the macro
definition, but specifications are much more general than macro
arguments. See Defining Macros, for more explanation of
the declare form.
You can also define an edebug specification for a macro separately
from the macro definition with def-edebug-spec. Adding
debug declarations is preferred, and more convenient, for macro
definitions in Lisp, but def-edebug-spec makes it possible to
define Edebug specifications for special forms implemented in C.
Specify which expressions of a call to macro macro are forms to be evaluated. specification should be the edebug specification. Neither argument is evaluated.
The macro argument can actually be any symbol, not just a macro name.
Here is a table of the possibilities for specification and how each directs processing of arguments.
t0If a macro has no Edebug specification, neither through a debug
declaration nor through a def-edebug-spec call, the variable
edebug-eval-macro-args comes into play.
This controls the way Edebug treats macro arguments with no explicit Edebug specification. If it is
nil(the default), none of the arguments is instrumented for evaluation. Otherwise, all arguments are instrumented.
A specification list is required for an Edebug specification if
some arguments of a macro call are evaluated while others are not. Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements. The latter, called
specification keywords, are symbols beginning with ‘&’ (such
as &optional).
A specification list may contain sublists which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Specification keywords apply only to the remainder of the sublist or group they are contained in.
When a specification list involves alternatives or repetition, matching it against an actual macro call may require backtracking. For more details, see Backtracking.
Edebug specifications provide the power of regular expression matching, plus some context-free grammar constructs: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via indirect specifications.
Here's a table of the possible elements of a specification list, with their meanings (see Specification Examples, for the referenced examples):
sexpformplacesetf construct.
body&rest form. See &rest below.
function-formquote rather than
function, since it instruments the body of the lambda expression
either way.
lambda-expr&optionalTo make just a few elements optional followed by non-optional elements,
use [&optional specs...]. To specify that several
elements must all match or none, use &optional
[specs...]. See the defun example.
&restTo repeat only a few elements, use [&rest specs...].
To specify several elements that must all match on every repetition, use
&rest [specs...].
&or&or
specification fails.
Each list element following &or is a single alternative. To
group two or more list elements as a single alternative, enclose them in
[...].
¬&or, but if any of them match, the specification fails. If none
of them match, nothing is matched, but the ¬ specification
succeeds.
&define&define keyword should be the first element in
a list specification.
nilgatelet example.
If the symbol has an Edebug specification, this indirect
specification should be either a list specification that is used in
place of the symbol, or a function that is called to process the
arguments. The specification may be defined with def-edebug-spec
just as for macros. See the defun example.
Otherwise, the symbol should be a predicate. The predicate is called
with the argument and the specification fails if the predicate returns
nil, and the argument is not instrumented.
Some suitable predicates include symbolp, integerp,
stringp, vectorp, and atom.
[elements...]"string"'symbol, where the name
of symbol is the string, but the string form is preferred.
(vector elements...)(elements...)A sublist specification may be a dotted list and the corresponding list
argument may then be a dotted list. Alternatively, the last cdr of a
dotted list specification may be another sublist specification (via a
grouping or an indirect specification, e.g., (spec . [(more
specs...)])) whose elements match the non-dotted list arguments.
This is useful in recursive specifications such as in the backquote
example. Also see the description of a nil specification
above for terminating such recursion.
Note that a sublist specification written as (specs . nil)
is equivalent to (specs), and (specs .
(sublist-elements...)) is equivalent to (specs
sublist-elements...).
Here is a list of additional specifications that may appear only after
&define. See the defun example.
nameA defining form is not required to have a name field; and it may have
multiple name fields.
:name:name should be a symbol; it is used as an additional
name component for the definition. You can use this to add a unique,
static component to the name of the definition. It may be used more
than once.
arglambda-listdef-bodybody, described above, but a definition body must be instrumented
with a different Edebug call that looks up information associated with
the definition. Use def-body for the highest level list of forms
within the definition.
def-formdef-body, except it is used to match a single form rather than
a list of forms. As a special case, def-form also means that
tracing information is not output when the form is executed. See the
interactive example.
If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, backtracking will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument.
When a syntax error is detected, it might not be reported until much
later, after higher-level alternatives have been exhausted, and with the
point positioned further from the real error. But if backtracking is
disabled when an error occurs, it can be reported immediately. Note
that backtracking is also reenabled automatically in several situations;
when a new alternative is established by &optional,
&rest, or &or, or at the start of processing a sublist,
group, or indirect specification. The effect of enabling or disabling
backtracking is limited to the remainder of the level currently being
processed and lower levels.
Backtracking is disabled while matching any of the
form specifications (that is, form, body, def-form, and
def-body). These specifications will match any form so any error
must be in the form itself rather than at a higher level.
Backtracking is also disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct. But if you have a set of alternative constructs that
all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
["foo" &or [first case] [second case] ...].
Most needs are satisfied by these two ways that backtracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the gate specification. This is
useful when you know that no higher alternatives could apply. See the
example of the let specification.
It may be easier to understand Edebug specifications by studying the examples provided here.
A let special form has a sequence of bindings and a body. Each
of the bindings is either a symbol or a sublist with a symbol and
optional expression. In the specification below, notice the gate
inside of the sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let
((&rest
&or symbolp (gate symbolp &optional form))
body))
Edebug uses the following specifications for defun and the
associated argument list and interactive specifications. It is
necessary to handle interactive forms specially since an expression
argument is actually evaluated outside of the function body. (The
specification for defmacro is very similar to that for
defun, but allows for the declare statement.)
(def-edebug-spec defun
(&define name lambda-list
[&optional stringp] ; Match the doc string, if present.
[&optional ("interactive" interactive)]
def-body))
(def-edebug-spec lambda-list
(([&rest arg]
[&optional ["&optional" arg &rest arg]]
&optional ["&rest" arg]
)))
(def-edebug-spec interactive
(&optional &or stringp def-form)) ; Notice: def-form
The specification for backquote below illustrates how to match
dotted lists and use nil to terminate recursion. It also
illustrates how components of a vector may be matched. (The actual
specification defined by Edebug is a little different, and does not
support dotted lists because doing so causes very deep recursion that
could fail.)
(def-edebug-spec \` (backquote-form)) ; Alias just for clarity.
(def-edebug-spec backquote-form
(&or ([&or "," ",@"] &or ("quote" backquote-form) form)
(backquote-form . [&or nil backquote-form])
(vector &rest backquote-form)
sexp))
These options affect the behavior of Edebug:
Functions to call before Edebug is used. Each time it is set to a new value, Edebug will call those functions once and then
edebug-setup-hookis reset tonil. You could use this to load up Edebug specifications associated with a package you are using but only when you also use Edebug. See Instrumenting.
If this is non-
nil, normal evaluation of defining forms such asdefunanddefmacroinstruments them for Edebug. This applies toeval-defun,eval-region,eval-buffer, andeval-current-buffer.Use the command M-x edebug-all-defs to toggle the value of this option. See Instrumenting.
If this is non-
nil, the commandseval-defun,eval-region,eval-buffer, andeval-current-bufferinstrument all forms, even those that don't define anything. This doesn't apply to loading or evaluations in the minibuffer.Use the command M-x edebug-all-forms to toggle the value of this option. See Instrumenting.
If this is non-
nil, Edebug saves and restores the window configuration. That takes some time, so if your program does not care what happens to the window configurations, it is better to set this variable tonil.If the value is a list, only the listed windows are saved and restored.
You can use the W command in Edebug to change this variable interactively. See Edebug Display Update.
If this is non-
nil, Edebug saves and restores point in all displayed buffers.Saving and restoring point in other buffers is necessary if you are debugging code that changes the point of a buffer that is displayed in a non-selected window. If Edebug or the user then selects the window, point in that buffer will move to the window's value of point.
Saving and restoring point in all buffers is expensive, since it requires selecting each window twice, so enable this only if you need it. See Edebug Display Update.
If this variable is non-
nil, it specifies the initial execution mode for Edebug when it is first activated. Possible values arestep,next,go,Go-nonstop,trace,Trace-fast,continue, andContinue-fast.The default value is
step. See Edebug Execution Modes.
If this is non-
nil, trace each function entry and exit. Tracing output is displayed in a buffer named ‘*edebug-trace*’, one function entry or exit per line, indented by the recursion level.Also see
edebug-tracing, in Trace Buffer.
If non-
nil, Edebug tests coverage of all expressions debugged. See Coverage Testing.
If non-
nil, continue defining or executing any keyboard macro that is executing outside of Edebug. Use this with caution since it is not debugged. See Edebug Execution Modes.
Edebug binds
debug-on-errorto this value, ifdebug-on-errorwas previouslynil. See Trapping Errors.
Edebug binds
debug-on-quitto this value, ifdebug-on-quitwas previouslynil. See Trapping Errors.
If you change the values of edebug-on-error or
edebug-on-quit while Edebug is active, their values won't be used
until the next time Edebug is invoked via a new command.
If non-
nil, an expression to test for at every stop point. If the result is non-nil, then break. Errors are ignored. See Global Break Condition.
The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error “End of file during parsing” in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, “Invalid read syntax: ")"” indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change?
If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases. (In addition, just moving point through the code with Show Paren mode enabled might find the mismatch.)
The first step is to find the defun that is unbalanced. If there is an excess open parenthesis, the way to do this is to go to the end of the file and type C-u C-M-u. This will move you to the beginning of the first defun that is unbalanced.
The next step is to determine precisely what is wrong. There is no way to be sure of this except by studying the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves. But don't do this yet! Keep reading, first.
Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use C-M-e to move there, since that too will fail to work until the defun is balanced.
Now you can go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
To deal with an excess close parenthesis, first go to the beginning of the file, then type C-u -1 C-M-u to find the end of the first unbalanced defun.
Then find the actual matching close parenthesis by typing C-M-f at the beginning of that defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity.
If you don't see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fits the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
You can do coverage testing for a file of Lisp code by loading the
testcover library and using the command M-x
testcover-start <RET> file <RET> to instrument the
code. Then test your code by calling it one or more times. Then use
the command M-x testcover-mark-all to display colored highlights
on the code to show where coverage is insufficient. The command
M-x testcover-next-mark will move point forward to the next
highlighted spot.
Normally, a red highlight indicates the form was never completely
evaluated; a brown highlight means it always evaluated to the same
value (meaning there has been little testing of what is done with the
result). However, the red highlight is skipped for forms that can't
possibly complete their evaluation, such as error. The brown
highlight is skipped for forms that are expected to always evaluate to
the same value, such as (setq x 14).
For difficult cases, you can add do-nothing macros to your code to give advice to the test coverage tool.
Evaluate form and return its value, but inform coverage testing that form's value should always be the same.
Evaluate form, informing coverage testing that form should never return. If it ever does return, you get a run-time error.
Edebug also has a coverage testing feature (see Coverage Testing). These features partly duplicate each other, and it would be cleaner to combine them.
When an error happens during byte compilation, it is normally due to invalid syntax in the program you are compiling. The compiler prints a suitable error message in the ‘*Compile-Log*’ buffer, and then stops. The message may state a function name in which the error was found, or it may not. Either way, here is how to find out where in the file the error occurred.
What you should do is switch to the buffer ‘ *Compiler Input*’. (Note that the buffer name starts with a space, so it does not show up in M-x list-buffers.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read.
If the error was due to invalid Lisp syntax, point shows exactly where the invalid syntax was detected. The cause of the error is not necessarily near by! Use the techniques in the previous section to find the error.
If the error was detected while compiling a form that had been read successfully, then point is located at the end of the form. In this case, this technique can't localize the error precisely, but can still show you which function to check.
Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in Lisp数据类型.
This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing).
Reading a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
read syntax of the object. For example, the text ‘(a . 5)’
is the read syntax for a cons cell whose car is a and whose
cdr is the number 5.
Printing a Lisp object means producing text that represents that object—converting the object to its printed representation (see 打印表示). Printing the cons cell described above produces the text ‘(a . 5)’.
Reading and printing are more or less inverse operations: printing the
object that results from reading a given piece of text often produces
the same text, and reading the text that results from printing an object
usually produces a similar-looking object. For example, printing the
symbol foo produces the text ‘foo’, and reading that text
returns the symbol foo. Printing a list whose elements are
a and b produces the text ‘(a b)’, and reading that
text produces a list (but not the same list) with elements a
and b.
However, these two operations are not precisely inverse to each other. There are three kinds of exceptions:
Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream:
tt used as a stream means that the input is read from the
minibuffer. In fact, the minibuffer is invoked once and the text
given by the user is made into a string that is then used as the
input stream. If Emacs is running in batch mode, standard input is used
instead of the minibuffer. For example,
(message "%s" (read t))
will read a Lisp expression from standard input and print the result
to standard output.
nilnil supplied as an input stream means to use the value of
standard-input instead; that value is the default input
stream, and must be a non-nil input stream.
Here is an example of reading from a stream that is a buffer, showing where point is located before and after:
---------- Buffer: foo ----------
This-!- is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
⇒ is
(read (get-buffer "foo"))
⇒ the
---------- Buffer: foo ----------
This is the-!- contents of foo.
---------- Buffer: foo ----------
Note that the first read skips a space. Reading skips any amount of whitespace preceding the significant text.
Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown. The value
read is the symbol This.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
⇒ #<marker at 1 in foo>
(read m)
⇒ This
m
⇒ #<marker at 5 in foo> ;; Before the first space.
Here we read from the contents of a string:
(read "(When in) the course")
⇒ (When in)
The following example reads from the minibuffer. The
prompt is: ‘Lisp expression: ’. (That is always the prompt
used when you read from the stream t.) The user's input is shown
following the prompt.
(read t)
⇒ 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 <RET>
---------- Buffer: Minibuffer ----------
Finally, here is an example of a stream that is a function, named
useless-stream. Before we use the stream, we initialize the
variable useless-list to a list of characters. Then each call to
the function useless-stream obtains the next character in the list
or unreads a character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))
⇒ (88 89 40 41)
(defun useless-stream (&optional unread)
(if unread
(setq useless-list (cons unread useless-list))
(prog1 (car useless-list)
(setq useless-list (cdr useless-list)))))
⇒ useless-stream
Now we read using the stream thus constructed:
(read 'useless-stream)
⇒ XY
useless-list
⇒ (40 41)
Note that the open and close parentheses remain in the list. The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it. Another attempt to read from the stream at this
point would read ‘()’ and return nil.
This function is used internally as an input stream to read from the input file opened by the function
load. Don't use this function yourself.
This section describes the Lisp functions and variables that pertain to reading.
In the functions below, stream stands for an input stream (see
the previous section). If stream is nil or omitted, it
defaults to the value of standard-input.
An end-of-file error is signaled if reading encounters an
unterminated list, vector, or string.
This function reads one textual Lisp expression from stream, returning it as a Lisp object. This is the basic Lisp input function.
This function reads the first textual Lisp expression from the text in string. It returns a cons cell whose car is that expression, and whose cdr is an integer giving the position of the next remaining character in the string (i.e., the first one not read).
If start is supplied, then reading begins at index start in the string (where the first character is at index 0). If you specify end, then reading is forced to stop just before that index, as if the rest of the string were not there.
For example:
(read-from-string "(setq x 55) (setq y 5)") ⇒ ((setq x 55) . 11) (read-from-string "\"A short string\"") ⇒ ("A short string" . 16) ;; Read starting at the first character. (read-from-string "(list 112)" 0) ⇒ ((list 112) . 10) ;; Read starting at the second character. (read-from-string "(list 112)" 1) ⇒ (list . 5) ;; Read starting at the seventh character, ;; and stopping at the ninth. (read-from-string "(list 112)" 6 8) ⇒ (11 . 8)
This variable holds the default input stream—the stream that
readuses when the stream argument isnil. The default ist, meaning use the minibuffer.
If non-
nil, this variable enables the reading of circular and shared structures. See 循环对象. Its default value ist.
An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream:
tnilnil specified as an output stream means to use the value of
standard-output instead; that value is the default output
stream, and must not be nil.
Many of the valid output streams are also valid as input streams. The difference between input and output streams is therefore more a matter of how you use a Lisp object, than of different types of object.
Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the ‘h’ in ‘the’. At the end, point is located directly before that same ‘h’.
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
⇒ "This is the output"
---------- Buffer: foo ----------
This is t
"This is the output"
-!-he contents of foo.
---------- Buffer: foo ----------
Now we show a use of a marker as an output stream. Initially, the
marker is in buffer foo, between the ‘t’ and the ‘h’ in
the word ‘the’. At the end, the marker has advanced over the
inserted text so that it remains positioned before the same ‘h’.
Note that the location of point, shown in the usual fashion, has no
effect.
---------- Buffer: foo ----------
This is the -!-output
---------- Buffer: foo ----------
(setq m (copy-marker 10))
⇒ #<marker at 10 in foo>
(print "More output for foo." m)
⇒ "More output for foo."
---------- Buffer: foo ----------
This is t
"More output for foo."
he -!-output
---------- Buffer: foo ----------
m
⇒ #<marker at 34 in foo>
The following example shows output to the echo area:
(print "Echo Area output" t)
⇒ "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------
Finally, we show the use of a function as an output stream. The
function eat-output takes each character that it is given and
conses it onto the front of the list last-output (see Building Lists). At the end, the list contains all the characters output, but
in reverse order.
(setq last-output nil)
⇒ nil
(defun eat-output (c)
(setq last-output (cons c last-output)))
⇒ eat-output
(print "This is the output" 'eat-output)
⇒ "This is the output"
last-output
⇒ (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:
(concat (nreverse last-output))
⇒ "
\"This is the output\"
"
Calling concat converts the list to a string so you can see its
contents more clearly.
This section describes the Lisp functions for printing Lisp objects—converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are ‘"’ and ‘\’; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See 打印表示, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints ‘#level’ instead of recursively printing an object already being printed. For example, here ‘#0’ indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil))
⇒ (nil)
(setcar foo foo)
⇒ (#0)
In the functions below, stream stands for an output stream.
(See the previous section for a description of output streams.) If
stream is nil or omitted, it defaults to the value of
standard-output.
The
(progn (print 'The\ cat\ in) (print "the hat") (print " came back")) -| -| The\ cat\ in -| -| "the hat" -| -| " came back" ⇒ " came back"
This function outputs the printed representation of object to stream. It does not print newlines to separate output as
(progn (prin1 'The\ cat\ in) (prin1 "the hat") (prin1 " came back")) -| The\ cat\ in"the hat"" came back" ⇒ " came back"
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people, not by
read, so it doesn't insert quoting characters and doesn't put double-quotes around the contents of strings. It does not add any spacing between calls.(progn (princ 'The\ cat) (princ " in the \"hat\"")) -| The cat in the "hat" ⇒ " in the \"hat\""
This function outputs a newline to stream. The name stands for “terminate print.”
This function outputs character to stream. It returns character.
This function returns a string containing the text that
prin1would have printed for the same argument.(prin1-to-string 'foo) ⇒ "foo" (prin1-to-string (mark-marker)) ⇒ "#<marker at 2773 in strings.texi>"If noescape is non-
nil, that inhibits use of quoting characters in the output. (This argument is supported in Emacs versions 19 and later.)(prin1-to-string "foo") ⇒ "\"foo\"" (prin1-to-string "foo" t) ⇒ "foo"See
format, in Formatting Strings, for other ways to obtain the printed representation of a Lisp object as a string.
This macro executes the body forms with
standard-outputset up to feed output into a string. Then it returns that string.For example, if the current buffer name is ‘foo’,
(with-output-to-string (princ "The buffer is ") (princ (buffer-name)))returns
"The buffer is foo".
The value of this variable is the default output stream—the stream that print functions use when the stream argument is
nil. The default ist, meaning display in the echo area.
If this is non-
nil, that means to print quoted forms using abbreviated reader syntax.(quote foo)prints as'foo,(function foo)as#'foo, and backquoted forms print using modern backquote syntax.
If this variable is non-
nil, then newline characters in strings are printed as ‘\n’ and formfeeds are printed as ‘\f’. Normally these characters are printed as actual newlines and formfeeds.This variable affects the print functions
prin1andprinc. Here is an example usingprin1:(prin1 "a\nb") -| "a -| b" ⇒ "a b" (let ((print-escape-newlines t)) (prin1 "a\nb")) -| "a\nb" ⇒ "a b"In the second expression, the local binding of
print-escape-newlinesis in effect during the call toprin1, but not during the printing of the result.
If this variable is non-
nil, then unibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functionsprin1andThose functions also use backslash sequences for unibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a multibyte buffer or a marker pointing into one.
If this variable is non-
nil, then multibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functionsprin1andThose functions also use backslash sequences for multibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a unibyte buffer or a marker pointing into one.
The value of this variable is the maximum number of elements to print in any list, vector or bool-vector. If an object being printed has more than this many elements, it is abbreviated with an ellipsis.
If the value is
nil(the default), then there is no limit.(setq print-length 2) ⇒ 2 (print '(1 2 3 4 5)) -| (1 2 ...) ⇒ (1 2 ...)
The value of this variable is the maximum depth of nesting of parentheses and brackets when printed. Any list or vector at a depth exceeding this limit is abbreviated with an ellipsis. A value of
nil(which is the default) means no limit.
These are the values for
print-lengthandprint-levelused byeval-expression, and thus, indirectly, by many interactive evaluation commands (see Evaluating Emacs-Lisp Expressions).
These variables are used for detecting and reporting circular and shared structure:
If non-
nil, this variable enables detection of circular and shared structure in printing. See 循环对象.
If non-
nil, this variable enables detection of uninterned symbols (see Creating Symbols) in printing. When this is enabled, uninterned symbols print with the prefix ‘#:’, which tells the Lisp reader to produce an uninterned symbol.
If non-
nil, that means number continuously across print calls. This affects the numbers printed for ‘#n=’ labels and ‘#m#’ references.Don't set this variable with
setq; you should only bind it temporarily totwithlet. When you do that, you should also bindprint-number-tabletonil.
This variable holds a vector used internally by printing to implement the
print-circlefeature. You should not use it except to bind it tonilwhen you bindprint-continuous-numbering.
This variable specifies how to print floating point numbers. Its default value is
nil, meaning use the shortest output that represents the number without losing information.To control output format more precisely, you can put a string in this variable. The string should hold a ‘%’-specification to be used in the C function
sprintf. For further restrictions on what you can use, see the variable's documentation string.
A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the frame, in the same place as the echo area (see The Echo Area), but only while it is in use for reading an argument.
In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ‘ *Minibuf-number*’, and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometimes frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see Minibuffers and Frames.)
The text in the minibuffer always starts with the prompt string,
the text that was specified by the program that is using the minibuffer
to tell the user what sort of input to type. This text is marked
read-only so you won't accidentally delete or change it. It is also
marked as a field (see Fields), so that certain motion functions,
including beginning-of-line, forward-word,
forward-sentence, and forward-paragraph, stop at the
boundary between the prompt and the actual text.
The minibuffer's window is normally a single line; it grows automatically if the contents require more space. You can explicitly resize it temporarily with the window sizing commands; it reverts to its normal size when the minibuffer is exited. You can resize it permanently by using the window sizing commands in the frame's other window, when the minibuffer is not active. If the frame contains just a minibuffer, you can change the minibuffer's size by changing the frame's size.
Use of the minibuffer reads input events, and that alters the values
of variables such as this-command and last-command
(see Command Loop Info). Your program should bind them around the
code that uses the minibuffer, if you do not want that to change them.
Under some circumstances, a command can use a minibuffer even if
there is an active minibuffer; such minibuffers are called a
recursive minibuffer. The first minibuffer is named
‘ *Minibuf-0*’. Recursive minibuffers are named by
incrementing the number at the end of the name. (The names begin with
a space so that they won't show up in normal buffer lists.) Of
several recursive minibuffers, the innermost (or most recently
entered) is the active minibuffer. We usually call this “the”
minibuffer. You can permit or forbid recursive minibuffers by setting
the variable enable-recursive-minibuffers, or by putting
properties of that name on command symbols (See Recursive Mini.)
Like other buffers, a minibuffer uses a local keymap (see Keymaps) to specify special key bindings. The function that invokes the minibuffer also sets up its local map according to the job to be done. See Text from Minibuffer, for the non-completion minibuffer local maps. See Completion Commands, for the minibuffer local maps for completion.
When Emacs is running in batch mode, any request to read from the minibuffer actually reads a line from the standard input descriptor that was supplied when Emacs was started.
The most basic primitive for minibuffer input is
read-from-minibuffer, which can be used to read either a string
or a Lisp object in textual form. The function read-regexp is
used for reading regular expressions (see Regular Expressions),
which are a special kind of string. There are also specialized
functions for reading commands, variables, file names, etc.
(see Completion).
In most cases, you should not call minibuffer input functions in the
middle of a Lisp function. Instead, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See Defining Commands.
This function is the most general way to get input from the minibuffer. By default, it accepts arbitrary text and returns it as a string; however, if read is non-
nil, then it usesreadto convert the text into a Lisp object (see Input Functions).The first thing this function does is to activate a minibuffer and display it with prompt-string as the prompt. This value must be a string. Then the user can edit text in the minibuffer.
When the user types a command to exit the minibuffer,
read-from-minibufferconstructs the return value from the text in the minibuffer. Normally it returns a string containing that text. However, if read is non-nil,read-from-minibufferreads the text and returns the resulting Lisp object, unevaluated. (See Input Functions, for information about reading.)The argument default specifies default values to make available through the history commands. It should be a string, a list of strings, or
nil. The string or strings become the minibuffer's “future history,” available to the user with M-n.If read is non-
nil, then default is also used as the input toread, if the user enters empty input. If default is a list of strings, the first string is used as the input. If default isnil, empty input results in anend-of-fileerror. However, in the usual case (where read isnil),read-from-minibufferignores default when the user enters empty input and returns an empty string,"". In this respect, it differs from all the other minibuffer input functions in this chapter.If keymap is non-
nil, that keymap is the local keymap to use in the minibuffer. If keymap is omitted ornil, the value ofminibuffer-local-mapis used as the keymap. Specifying a keymap is the most important way to customize the minibuffer for various applications such as completion.The argument hist specifies which history list variable to use for saving the input and for history commands used in the minibuffer. It defaults to
minibuffer-history. See Minibuffer History.If the variable
minibuffer-allow-text-propertiesis non-nil, then the string which is returned includes whatever text properties were present in the minibuffer. Otherwise all the text properties are stripped when the value is returned.If the argument inherit-input-method is non-
nil, then the minibuffer inherits the current input method (see Input Methods) and the setting ofenable-multibyte-characters(see Text Representations) from whichever buffer was current before entering the minibuffer.Use of initial-contents is mostly deprecated; we recommend using a non-
nilvalue only in conjunction with specifying a cons cell for hist. See Initial Input.
This function reads a string from the minibuffer and returns it. The arguments prompt, initial, history and inherit-input-method are used as in
read-from-minibuffer. The keymap used isminibuffer-local-map.The optional argument default is used as in
read-from-minibuffer, except that, if non-nil, it also specifies a default value to return if the user enters null input. As inread-from-minibufferit should be a string, a list of strings, ornilwhich is equivalent to an empty string. When default is a string, that string is the default value. When it is a list of strings, the first string is the default value. (All these strings are available to the user in the “future minibuffer history.”)This function works by calling the
read-from-minibufferfunction:(read-string prompt initial history default inherit) == (let ((value (read-from-minibuffer prompt initial nil nil history default inherit))) (if (and (equal value "") default) (if (consp default) (car default) default) value))
This function reads a regular expression as a string from the minibuffer and returns it. The argument prompt is used as in
read-from-minibuffer. The keymap used isminibuffer-local-map, andregexp-historyis used as the history list (see regexp-history).The optional argument default-value specifies a default value to return if the user enters null input; it should be a string, or
nilwhich is equivalent to an empty string.In addition,
read-regexpcollects a few useful candidates for input and passes them toread-from-minibuffer, to make them available to the user as the “future minibuffer history list” (see future list). These candidates are:
- The word or symbol at point.
- The last regexp used in an incremental search.
- The last string used in an incremental search.
- The last string or pattern used in query-replace commands.
This function works by calling the
read-from-minibufferfunction, after computing the list of defaults as described above.
If this variable is
nil, thenread-from-minibufferstrips all text properties from the minibuffer input before returning it. This variable also affectsread-string. However,read-no-blanks-input(see below), as well asread-minibufferand related functions (see Reading Lisp Objects With the Minibuffer), and all functions that do minibuffer input with completion, discard text properties unconditionally, regardless of the value of this variable.
This is the default local keymap for reading from the minibuffer. By default, it makes the following bindings:
- C-j
exit-minibuffer- <RET>
exit-minibuffer- C-g
abort-recursive-edit- M-n
- <DOWN>
next-history-element- M-p
- <UP>
previous-history-element- M-s
next-matching-history-element- M-r
previous-matching-history-element
This function reads a string from the minibuffer, but does not allow whitespace characters as part of the input: instead, those characters terminate the input. The arguments prompt, initial, and inherit-input-method are used as in
read-from-minibuffer.This is a simplified interface to the
read-from-minibufferfunction, and passes the value of theminibuffer-local-ns-mapkeymap as the keymap argument for that function. Since the keymapminibuffer-local-ns-mapdoes not rebind C-q, it is possible to put a space into the string, by quoting it.This function discards text properties, regardless of the value of
minibuffer-allow-text-properties.(read-no-blanks-input prompt initial) == (let (minibuffer-allow-text-properties) (read-from-minibuffer prompt initial minibuffer-local-ns-map))
This built-in variable is the keymap used as the minibuffer local keymap in the function
read-no-blanks-input. By default, it makes the following bindings, in addition to those ofminibuffer-local-map:
This section describes functions for reading Lisp objects with the minibuffer.
This function reads a Lisp object using the minibuffer, and returns it without evaluating it. The arguments prompt and initial are used as in
read-from-minibuffer.This is a simplified interface to the
read-from-minibufferfunction:(read-minibuffer prompt initial) == (let (minibuffer-allow-text-properties) (read-from-minibuffer prompt initial nil t))Here is an example in which we supply the string
"(testing)"as initial input:(read-minibuffer "Enter an expression: " (format "%s" '(testing))) ;; Here is how the minibuffer is displayed: ---------- Buffer: Minibuffer ---------- Enter an expression: (testing)-!- ---------- Buffer: Minibuffer ----------The user can type <RET> immediately to use the initial input as a default, or can edit the input.
This function reads a Lisp expression using the minibuffer, evaluates it, then returns the result. The arguments prompt and initial are used as in
read-from-minibuffer.This function simply evaluates the result of a call to
read-minibuffer:(eval-minibuffer prompt initial) == (eval (read-minibuffer prompt initial))
This function reads a Lisp expression in the minibuffer, and then evaluates it. The difference between this command and
eval-minibufferis that here the initial form is not optional and it is treated as a Lisp object to be converted to printed representation rather than as a string of text. It is printed withprin1, so if it is a string, double-quote characters (‘"’) appear in the initial text. See Output Functions.The first thing
edit-and-eval-commanddoes is to activate the minibuffer with prompt as the prompt. Then it inserts the printed representation of form in the minibuffer, and lets the user edit it. When the user exits the minibuffer, the edited text is read withreadand then evaluated. The resulting value becomes the value ofedit-and-eval-command.In the following example, we offer the user an expression with initial text which is a valid form already:
(edit-and-eval-command "Please edit: " '(forward-word 1)) ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Please edit: (forward-word 1)-!- ---------- Buffer: Minibuffer ----------Typing <RET> right away would exit the minibuffer and evaluate the expression, thus moving point forward one word.
edit-and-eval-commandreturnsnilin this example.
A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. A history list is actually a symbol, not a list; it is a variable whose value is a list of strings (previous inputs), most recent first.
There are many separate history lists, used for different kinds of inputs. It's the Lisp programmer's job to specify the right history list for each use of the minibuffer.
You specify the history list with the optional hist argument
to either read-from-minibuffer or completing-read. Here
are the possible values for it:
Specifying 0 for startpos is equivalent to just specifying the
symbol variable. previous-history-element will display
the most recent element of the history list in the minibuffer. If you
specify a positive startpos, the minibuffer history functions
behave as if (elt variable (1- STARTPOS)) were the
history element currently shown in the minibuffer.
For consistency, you should also specify that element of the history as the initial minibuffer contents, using the initial argument to the minibuffer input function (see Initial Input).
If you don't specify hist, then the default history list
minibuffer-history is used. For other standard history lists,
see below. You can also create your own history list variable; just
initialize it to nil before the first use.
Both read-from-minibuffer and completing-read add new
elements to the history list automatically, and provide commands to
allow the user to reuse items on the list. The only thing your program
needs to do to use a history list is to initialize it and to pass its
name to the input functions when you wish. But it is safe to modify the
list by hand when the minibuffer input functions are not using it.
Emacs functions that add a new element to a history list can also
delete old elements if the list gets too long. The variable
history-length specifies the maximum length for most history
lists. To specify a different maximum length for a particular history
list, put the length in the history-length property of the
history list symbol. The variable history-delete-duplicates
specifies whether to delete duplicates in history.
This function adds a new element newelt, if it isn't the empty string, to the history list stored in the variable history-var, and returns the updated history list. It limits the list length to the value of maxelt (if non-
nil) orhistory-length(described below). The possible values of maxelt have the same meaning as the values ofhistory-length.Normally,
add-to-historyremoves duplicate members from the history list ifhistory-delete-duplicatesis non-nil. However, if keep-all is non-nil, that says not to remove duplicates, and to add newelt to the list even if it is empty.
If the value of this variable is
nil, standard functions that read from the minibuffer don't add new elements to the history list. This lets Lisp programs explicitly manage input history by usingadd-to-history. By default,history-add-new-inputis set to a non-nilvalue.
The value of this variable specifies the maximum length for all history lists that don't specify their own maximum lengths. If the value is
t, that means there is no maximum (don't delete old elements). The value ofhistory-lengthproperty of the history list variable's symbol, if set, overrides this variable for that particular history list.
If the value of this variable is
t, that means when adding a new history element, all previous identical elements are deleted.
Here are some of the standard minibuffer history list variables:
A history list for arguments to
query-replace(and similar arguments to other commands).
A history list for arguments that are names of extended commands.
A history list for arguments that are Lisp expressions to evaluate.
Several of the functions for minibuffer input have an argument called initial or initial-contents. This is a mostly-deprecated feature for specifying that the minibuffer should start out with certain text, instead of empty as usual.
If initial is a string, the minibuffer starts out containing the text of the string, with point at the end, when the user starts to edit the text. If the user simply types <RET> to exit the minibuffer, it will use the initial input string to determine the value to return.
We discourage use of a non-nil value for
initial, because initial input is an intrusive interface.
History lists and default values provide a much more convenient method
to offer useful default inputs to the user.
There is just one situation where you should specify a string for an initial argument. This is when you specify a cons cell for the hist or history argument. See Minibuffer History.
initial can also be a cons cell of the form (string
. position). This means to insert string in the
minibuffer but put point at position within the string's text.
As a historical accident, position was implemented
inconsistently in different functions. In completing-read,
position's value is interpreted as origin-zero; that is, a value
of 0 means the beginning of the string, 1 means after the first
character, etc. In read-minibuffer, and the other
non-completion minibuffer input functions that support this argument,
1 means the beginning of the string 2 means after the first character,
etc.
Use of a cons cell as the value for initial arguments is deprecated in user code.
Completion is a feature that fills in the rest of a name
starting from an abbreviation for it. Completion works by comparing the
user's input against a list of valid names and determining how much of
the name is determined uniquely by what the user has typed. For
example, when you type C-x b (switch-to-buffer) and then
type the first few letters of the name of the buffer to which you wish
to switch, and then type <TAB> (minibuffer-complete), Emacs
extends the name as far as it can.
Standard Emacs commands offer completion for names of symbols, files, buffers, and processes; with the functions in this section, you can implement completion for other kinds of names.
The try-completion function is the basic primitive for
completion: it returns the longest determined completion of a given
initial string, with a given set of strings to match against.
The function completing-read provides a higher-level interface
for completion. A call to completing-read specifies how to
determine the list of valid names. The function then activates the
minibuffer with a local keymap that binds a few keys to commands useful
for completion. Other functions provide convenient simple interfaces
for reading certain kinds of names with completion.
The following completion functions have nothing in themselves to do with minibuffers. We describe them here to keep them near the higher-level completion features that do use the minibuffer.
This function returns the longest common substring of all possible completions of string in collection. The value of collection must be a list of strings or symbols, an alist, an obarray, a hash table, or a completion function (see Programmed Completion).
Completion compares string against each of the permissible completions specified by collection. If no permissible completions match,
try-completionreturnsnil. If there is just one matching completion, and the match is exact, it returnst. Otherwise, it returns the longest initial sequence common to all possible matching completions.If collection is an alist (see Association Lists), the permissible completions are the elements of the alist that are either strings, symbols, or conses whose car is a string or symbol. Symbols are converted to strings using
symbol-name. Other elements of the alist are ignored. (Remember that in Emacs Lisp, the elements of alists do not have to be conses.) In particular, a list of strings or symbols is allowed, even though we usually do not think of such lists as alists.If collection is an obarray (see Creating Symbols), the names of all symbols in the obarray form the set of permissible completions. The global variable
obarrayholds an obarray containing the names of all interned Lisp symbols.Note that the only valid way to make a new obarray is to create it empty and then add symbols to it one by one using
intern. Also, you cannot intern a given symbol in more than one obarray.If collection is a hash table, then the keys that are strings are the possible completions. Other keys are ignored.
You can also use a symbol that is a function as collection. Then the function is solely responsible for performing completion;
try-completionreturns whatever this function returns. The function is called with three arguments: string, predicate andnil(the reason for the third argument is so that the same function can be used inall-completionsand do the appropriate thing in either case). See Programmed Completion.If the argument predicate is non-
nil, then it must be a function of one argument, unless collection is a hash table, in which case it should be a function of two arguments. It is used to test each possible match, and the match is accepted only if predicate returns non-nil. The argument given to predicate is either a string or a cons cell (the car of which is a string) from the alist, or a symbol (not a symbol name) from the obarray. If collection is a hash table, predicate is called with two arguments, the string key and the associated value.In addition, to be acceptable, a completion must also match all the regular expressions in
completion-regexp-list. (Unless collection is a function, in which case that function has to handlecompletion-regexp-listitself.)In the first of the following examples, the string ‘foo’ is matched by three of the alist cars. All of the matches begin with the characters ‘fooba’, so that is the result. In the second example, there is only one possible match, and it is exact, so the value is
t.(try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))) ⇒ "fooba" (try-completion "foo" '(("barfoo" 2) ("foo" 3))) ⇒ tIn the following example, numerous symbols begin with the characters ‘forw’, and all of them begin with the word ‘forward’. In most of the symbols, this is followed with a ‘-’, but not in all, so no more than ‘forward’ can be completed.
(try-completion "forw" obarray) ⇒ "forward"Finally, in the following example, only two of the three possible matches pass the predicate
test(the string ‘foobaz’ is too short). Both of those begin with the string ‘foobar’.(defun test (s) (> (length (car s)) 6)) ⇒ test (try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) ⇒ "foobar"
This function returns a list of all possible completions of string. The arguments to this function (aside from nospace) are the same as those of
try-completion. Also, this function usescompletion-regexp-listin the same way thattry-completiondoes.The optional argument nospace is obsolete. If it is non-
nil, completions that start with a space are ignored unless string starts with a space.If collection is a function, it is called with three arguments: string, predicate and
t; thenall-completionsreturns whatever the function returns. See Programmed Completion.Here is an example, using the function
testshown in the example fortry-completion:(defun test (s) (> (length (car s)) 6)) ⇒ test (all-completions "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) ⇒ ("foobar1" "foobar2")
This function returns non-
nilif string is a valid completion possibility specified by collection and predicate. The arguments are the same as intry-completion. For instance, if collection is a list of strings, this is true if string appears in the list and predicate is satisfied.This function uses
completion-regexp-listin the same way thattry-completiondoes.If predicate is non-
niland if collection contains several strings that are equal to each other, as determined bycompare-stringsaccording tocompletion-ignore-case, then predicate should accept either all or none of them. Otherwise, the return value oftest-completionis essentially unpredictable.If collection is a function, it is called with three arguments, the values string, predicate and
lambda; whatever it returns,test-completionreturns in turn.
This function returns the boundaries of the field on which collection will operate, assuming that string holds the text before point and suffix holds the text after point.
Normally completion operates on the whole string, so for all normal collections, this will always return
(0 . (lengthsuffix)). But more complex completion such as completion on files is done one field at a time. For example, completion of"/usr/sh"will include"/usr/share/"but not"/usr/share/doc"even if"/usr/share/doc"exists. Alsoall-completionson"/usr/sh"will not include"/usr/share/"but only"share/". So if string is"/usr/sh"and suffix is"e/doc",completion-boundarieswill return(5 . 1)which tells us that the collection will only return completion information that pertains to the area after"/usr/"and before"/doc".
If you store a completion alist in a variable, you should mark the
variable as “risky” with a non-nil
risky-local-variable property. See File Local Variables.
If the value of this variable is non-
nil, Emacs does not consider case significant in completion. Note, however, that this variable is overridden byread-file-name-completion-ignore-casewithinread-file-name(see Reading File Names), and byread-buffer-completion-ignore-casewithinread-buffer(see High-Level Completion).
This is a list of regular expressions. The completion functions only consider a completion acceptable if it matches all regular expressions in this list, with
case-fold-search(see Searching and Case) bound to the value ofcompletion-ignore-case.
This macro provides a way to initialize the variable var as a collection for completion in a lazy way, not computing its actual contents until they are first needed. You use this macro to produce a value that you store in var. The actual computation of the proper value is done the first time you do completion using var. It is done by calling fun with no arguments. The value fun returns becomes the permanent value of var.
Here is an example of use:
(defvar foo (lazy-completion-table foo make-my-alist))
The function completion-in-region provides a convenient way to
perform completion on an arbitrary stretch of text in an Emacs buffer:
This function completes the text in the current buffer between the positions start and end, using collection. The argument collection has the same meaning as in
try-completion(see Basic Completion).This function inserts the completion text directly into the current buffer. Unlike
completing-read(see Minibuffer Completion), it does not activate the minibuffer.For this function to work, point must be somewhere between start and end.
This section describes the basic interface for reading from the minibuffer with completion.
This function reads a string in the minibuffer, assisting the user by providing completion. It activates the minibuffer with prompt prompt, which must be a string.
The actual completion is done by passing collection and predicate to the function
try-completion(see Basic Completion). This happens in certain commands bound in the local keymaps used for completion. Some of these commands also calltest-completion. Thus, if predicate is non-nil, it should be compatible with collection andcompletion-ignore-case. See Definition of test-completion.The value of the optional argument require-match determines how the user may exit the minibuffer:
- If
nil, the usual minibuffer exit commands work regardless of the input in the minibuffer.- If
t, the usual minibuffer exit commands won't exit unless the input completes to an element of collection.- If
confirm, the user can exit with any input, but is asked for confirmation if the input is not an element of collection.- If
confirm-after-completion, the user can exit with any input, but is asked for confirmation if the preceding command was a completion command (i.e., one of the commands inminibuffer-confirm-exit-commands) and the resulting input is not an element of collection. See Completion Commands.- Any other value of require-match behaves like
t, except that the exit commands won't exit if it performs completion.However, empty input is always permitted, regardless of the value of require-match; in that case,
completing-readreturns the first element of default, if it is a list;"", if default isnil; or default. The string or strings in default are also available to the user through the history commands.The function
completing-readusesminibuffer-local-completion-mapas the keymap if require-match isnil, and usesminibuffer-local-must-match-mapif require-match is non-nil. See Completion Commands.The argument hist specifies which history list variable to use for saving the input and for minibuffer history commands. It defaults to
minibuffer-history. See Minibuffer History.The argument initial is mostly deprecated; we recommend using a non-
nilvalue only in conjunction with specifying a cons cell for hist. See Initial Input. For default input, use default instead.If the argument inherit-input-method is non-
nil, then the minibuffer inherits the current input method (see Input Methods) and the setting ofenable-multibyte-characters(see Text Representations) from whichever buffer was current before entering the minibuffer.If the built-in variable
completion-ignore-caseis non-nil, completion ignores case when comparing the input against the possible matches. See Basic Completion. In this mode of operation, predicate must also ignore case, or you will get surprising results.Here's an example of using
completing-read:(completing-read "Complete a foo: " '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) nil t "fo") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Complete a foo: fo-!- ---------- Buffer: Minibuffer ----------If the user then types <DEL> <DEL> b <RET>,
completing-readreturnsbarfoo.The
completing-readfunction binds variables to pass information to the commands that actually do completion. They are described in the following section.
This section describes the keymaps, commands and user options used in the minibuffer to do completion.
The value of this variable is the collection used for completion in the minibuffer. This is the global variable that contains what
completing-readpasses totry-completion. It is used by minibuffer completion commands such asminibuffer-complete-word.
This variable's value is the predicate that
completing-readpasses totry-completion. The variable is also used by the other minibuffer completion functions.
This variable determines whether Emacs asks for confirmation before exiting the minibuffer;
completing-readbinds this variable, and the functionminibuffer-complete-and-exitchecks the value before exiting. If the value isnil, confirmation is not required. If the value isconfirm, the user may exit with an input that is not a valid completion alternative, but Emacs asks for confirmation. If the value isconfirm-after-completion, the user may exit with an input that is not a valid completion alternative, but Emacs asks for confirmation if the user submitted the input right after any of the completion commands inminibuffer-confirm-exit-commands.
This variable holds a list of commands that cause Emacs to ask for confirmation before exiting the minibuffer, if the require-match argument to
completing-readisconfirm-after-completion. The confirmation is requested if the user attempts to exit the minibuffer immediately after calling any command in this list.
This function completes the minibuffer contents by at most a single word. Even if the minibuffer contents have only one completion,
minibuffer-complete-worddoes not add any characters beyond the first character that is not a word constituent. See Syntax Tables.
This function completes the minibuffer contents, and exits if confirmation is not required, i.e., if
minibuffer-completion-confirmisnil. If confirmation is required, it is given by repeating this command immediately—the command is programmed to work without confirmation when run twice in succession.
This function creates a list of the possible completions of the current minibuffer contents. It works by calling
all-completionsusing the value of the variableminibuffer-completion-tableas the collection argument, and the value ofminibuffer-completion-predicateas the predicate argument. The list of completions is displayed as text in a buffer named ‘*Completions*’.
This function displays completions to the stream in
standard-output, usually a buffer. (See Read and Print, for more information about streams.) The argument completions is normally a list of completions just returned byall-completions, but it does not have to be. Each element may be a symbol or a string, either of which is simply printed. It can also be a list of two strings, which is printed as if the strings were concatenated. The first of the two strings is the actual completion, the second string serves as annotation.The argument common-substring is the prefix that is common to all the completions. With normal Emacs completion, it is usually the same as the string that was completed.
display-completion-listuses this to highlight text in the completion list for better visual feedback. This is not needed in the minibuffer; for minibuffer completion, you can passnil.This function is called by
minibuffer-completion-help. The most common way to use it is together withwith-output-to-temp-buffer, like this:(with-output-to-temp-buffer "*Completions*" (display-completion-list (all-completions (buffer-string) my-alist) (buffer-string)))
If this variable is non-
nil, the completion commands automatically display a list of possible completions whenever nothing can be completed because the next character is not uniquely determined.
completing-readuses this value as the local keymap when an exact match of one of the completions is not required. By default, this keymap makes the following bindings:
- ?
minibuffer-completion-help- <SPC>
minibuffer-complete-word- <TAB>
minibuffer-completewith other characters bound as in
minibuffer-local-map(see Definition of minibuffer-local-map).
completing-readuses this value as the local keymap when an exact match of one of the completions is required. Therefore, no keys are bound toexit-minibuffer, the command that exits the minibuffer unconditionally. By default, this keymap makes the following bindings:
- ?
minibuffer-completion-help- <SPC>
minibuffer-complete-word- <TAB>
minibuffer-complete- C-j
minibuffer-complete-and-exit- <RET>
minibuffer-complete-and-exitwith other characters bound as in
minibuffer-local-map.
This is like
minibuffer-local-completion-mapexcept that it does not bind <SPC>. This keymap is used by the functionread-file-name.
This is like
minibuffer-local-must-match-mapexcept that it does not bind <SPC>. This keymap is used by the functionread-file-name.
This section describes the higher-level convenient functions for reading certain sorts of names with completion.
In most cases, you should not call these functions in the middle of a
Lisp function. When possible, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See Defining Commands.
This function reads the name of a buffer and returns it as a string. The argument default is the default name to use, the value to return if the user exits with an empty minibuffer. If non-
nil, it should be a string, a list of strings, or a buffer. If it is a list, the default value is the first element of this list. It is mentioned in the prompt, but is not inserted in the minibuffer as initial input.The argument prompt should be a string ending with a colon and a space. If default is non-
nil, the function inserts it in prompt before the colon to follow the convention for reading from the minibuffer with a default value (see Programming Tips).The optional argument require-match has the same meaning as in
completing-read. See Minibuffer Completion.In the following example, the user enters ‘minibuffer.t’, and then types <RET>. The argument require-match is
t, and the only buffer name starting with the given input is ‘minibuffer.texi’, so that name is the value.(read-buffer "Buffer name: " "foo" t) ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Buffer name (default foo): -!- ---------- Buffer: Minibuffer ---------- ;; The user types minibuffer.t <RET>. ⇒ "minibuffer.texi"
This variable specifies how to read buffer names. The function is called with the arguments passed to
read-buffer. For example, if you set this variable toiswitchb-read-buffer, all Emacs commands that callread-bufferto read a buffer name will actually use theiswitchbpackage to read it.
If this variable is non-
nil,read-bufferignores case when performing completion.
This function reads the name of a command and returns it as a Lisp symbol. The argument prompt is used as in
read-from-minibuffer. Recall that a command is anything for whichcommandpreturnst, and a command name is a symbol for whichcommandpreturnst. See Interactive Call.The argument default specifies what to return if the user enters null input. It can be a symbol, a string or a list of strings. If it is a string,
read-commandinterns it before returning it. If it is a list,read-commandreturns the first element of this list. If default isnil, that means no default has been specified; then if the user enters null input, the return value is(intern ""), that is, a symbol whose name is an empty string.(read-command "Command name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Command name? ---------- Buffer: Minibuffer ----------If the user types forward-c <RET>, then this function returns
forward-char.The
read-commandfunction is a simplified interface tocompleting-read. It uses the variableobarrayso as to complete in the set of extant Lisp symbols, and it uses thecommandppredicate so as to accept only command names:(read-command prompt) == (intern (completing-read prompt obarray 'commandp t nil))
This function reads the name of a user variable and returns it as a symbol.
The argument default specifies the default value to return if the user enters null input. It can be a symbol, a string, or a list of strings. If it is a string,
read-variableinterns it to make the default value. If it is a list,read-variableinterns the first element. If default isnil, that means no default has been specified; then if the user enters null input, the return value is(intern "").(read-variable "Variable name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Variable name? -!- ---------- Buffer: Minibuffer ----------If the user then types fill-p <RET>,
read-variablereturnsfill-prefix.In general,
read-variableis similar toread-command, but uses the predicateuser-variable-pinstead ofcommandp:(read-variable prompt) == (intern (completing-read prompt obarray 'user-variable-p t nil))
This function reads a string that is a color specification, either the color's name or an RGB hex value such as
#RRRGGGBBB. It prompts with prompt (default:"Color (name or #R+G+B+):") and provides completion for color names, but not for hex RGB values. In addition to names of standard colors, completion candidates include the foreground and background colors at point.Valid RGB values are described in Color Names.
The function's return value is the color name typed by the user in the minibuffer. However, when called interactively or if the optional argument convert is non-
nil, it converts the name into the color's RGB value and returns that value as a string. If an invalid color name was specified, this function signals an error, except that empty color names are allowed whenallow-emptyis non-niland the user enters null input.Interactively, or when display is non-
nil, the return value is also displayed in the echo area.
See also the functions read-coding-system and
read-non-nil-coding-system, in User-Chosen Coding Systems,
and read-input-method-name, in Input Methods.
The high-level completion functions read-file-name,
read-directory-name, and read-shell-command are designed
to read file names, directory names, and shell commands respectively.
They provide special features, including automatic insertion of the
default directory.
This function reads a file name, prompting with prompt and providing completion.
As an exception, this function reads a file name using a graphical file dialog instead of the minibuffer, if (i) it is invoked via a mouse command, and (ii) the selected frame is on a graphical display supporting such dialogs, and (iii) the variable
use-dialog-boxis non-nil(see Dialog Boxes), and (iv) the directory argument, described below, does not specify a remote file (see Remote Files). The exact behavior when using a graphical file dialog is platform-dependent. Here, we simply document the behavior when using the minibuffer.The optional argument require-match has the same meaning as in
completing-read. See Minibuffer Completion.
read-file-nameusesminibuffer-local-filename-completion-mapas the keymap if require-match isnil, and usesminibuffer-local-filename-must-match-mapif require-match is non-nil. See Completion Commands.The argument directory specifies the directory to use for completion of relative file names. It should be an absolute directory name. If
insert-default-directoryis non-nil, directory is also inserted in the minibuffer as initial input. It defaults to the current buffer's value ofdefault-directory.If you specify initial, that is an initial file name to insert in the buffer (after directory, if that is inserted). In this case, point goes at the beginning of initial. The default for initial is
nil—don't insert any file name. To see what initial does, try the command C-x C-v. Please note: we recommend using default rather than initial in most cases.If default is non-
nil, then the function returns default if the user exits the minibuffer with the same non-empty contents thatread-file-nameinserted initially. The initial minibuffer contents are always non-empty ifinsert-default-directoryis non-nil, as it is by default. default is not checked for validity, regardless of the value of require-match. However, if require-match is non-nil, the initial minibuffer contents should be a valid file (or directory) name. Otherwiseread-file-nameattempts completion if the user exits without any editing, and does not return default. default is also available through the history commands.If default is
nil,read-file-nametries to find a substitute default to use in its place, which it treats in exactly the same way as if it had been specified explicitly. If default isnil, but initial is non-nil, then the default is the absolute file name obtained from directory and initial. If both default and initial areniland the buffer is visiting a file,read-file-nameuses the absolute file name of that file as default. If the buffer is not visiting a file, then there is no default. In that case, if the user types <RET> without any editing,read-file-namesimply returns the pre-inserted contents of the minibuffer.If the user types <RET> in an empty minibuffer, this function returns an empty string, regardless of the value of require-match. This is, for instance, how the user can make the current buffer visit no file using
M-x set-visited-file-name.If predicate is non-
nil, it specifies a function of one argument that decides which file names are acceptable completion possibilities. A file name is an acceptable value if predicate returns non-nilfor it.
read-file-namedoes not automatically expand file names. You must callexpand-file-nameyourself if an absolute file name is required.Here is an example:
(read-file-name "The file is ") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/-!- ---------- Buffer: Minibuffer ----------Typing manual <TAB> results in the following:
---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/manual.texi-!- ---------- Buffer: Minibuffer ----------If the user types <RET>,
read-file-namereturns the file name as the string"/gp/gnu/elisp/manual.texi".
If non-
nil, this should be a function that accepts the same arguments asread-file-name. Whenread-file-nameis called, it calls this function with the supplied arguments instead of doing its usual work.
If this variable is non-
nil,read-file-nameignores case when performing completion.
This function is like
read-file-namebut allows only directory names as completion possibilities.If default is
niland initial is non-nil,read-directory-nameconstructs a substitute default by combining directory (or the current buffer's default directory if directory isnil) and initial. If both default and initial arenil, this function uses directory as substitute default, or the current buffer's default directory if directory isnil.
This variable is used by
read-file-name, and thus, indirectly, by most commands reading file names. (This includes all commands that use the code letters ‘f’ or ‘F’ in their interactive form. See Code Characters for interactive.) Its value controls whetherread-file-namestarts by placing the name of the default directory in the minibuffer, plus the initial file name if any. If the value of this variable isnil, thenread-file-namedoes not place any initial input in the minibuffer (unless you specify initial input with the initial argument). In that case, the default directory is still used for completion of relative file names, but is not displayed.If this variable is
niland the initial minibuffer contents are empty, the user may have to explicitly fetch the next history element to access a default value. If the variable is non-nil, the initial minibuffer contents are always non-empty and the user can always request a default value by immediately typing <RET> in an unedited minibuffer. (See above.)For example:
;; Here the minibuffer starts out with the default directory. (let ((insert-default-directory t)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is ~lewis/manual/-!- ---------- Buffer: Minibuffer ---------- ;; Here the minibuffer is empty and only the prompt ;; appears on its line. (let ((insert-default-directory nil)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is -!- ---------- Buffer: Minibuffer ----------
This function reads a shell command from the minibuffer, prompting with prompt and providing intelligent completion. It completes the first word of the command using candidates that are appropriate for command names, and the rest of the command words as file names.
This function uses
minibuffer-local-shell-command-mapas the keymap for minibuffer input. The hist argument specifies the history list to use; if is omitted ornil, it defaults toshell-command-history(see shell-command-history). The optional argument initial-contents specifies the initial content of the minibuffer (see Initial Input). The rest of args, if present, are used as the default and inherit-input-method arguments inread-from-minibuffer(see Text from Minibuffer).
This keymap is used by
read-shell-commandfor completing command and file names that are part of a shell command.
A completion style is a set of rules for generating
completions. The user option completion-styles stores a list
of completion styles, which are represented by symbols.
This is a list of completion style symbols to use for performing completion. Each completion style in this list must be defined in
completion-styles-alist.
This variable stores a list of available completion styles. Each element in the list must have the form ‘(name try-completion all-completions)’. Here, name is the name of the completion style (a symbol), which may be used in
completion-styles-alistto refer to this style.try-completion is the function that does the completion, and all-completions is the function that lists the completions. These functions should accept four arguments: string, collection, predicate, and point. The string, collection, and predicate arguments have the same meanings as in
try-completion(see Basic Completion), and the point argument is the position of point within string. Each function should return a non-nilvalue if it performed its job, andnilif it did not (e.g., if there is no way to complete string according to the completion style).When the user calls a completion command, such as
minibuffer-complete(see Completion Commands), Emacs looks for the first style listed incompletion-stylesand calls its try-completion function. If this function returnsnil, Emacs moves to the next completion style listed incompletion-stylesand calls its try-completion function, and so on until one of the try-completion functions successfully performs completion and returns a non-nilvalue. A similar procedure is used for listing completions, via the all-completions functions.
By default, completion-styles-alist contains five pre-defined
completion styles: basic, a basic completion style;
partial-completion, which does partial completion (completing
each word in the input separately); emacs22, which performs
completion according to the rules used in Emacs 22; emacs21,
which performs completion according to the rules used in Emacs 21; and
initials, which completes acronyms and initialisms.
Sometimes it is not possible to create an alist or an obarray containing all the intended possible completions. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion. Emacs uses programmed completion when completing file names (see File Name Completion), among many other cases.
To use this feature, pass a function as the collection
argument to completing-read. The function
completing-read arranges to pass your completion function along
to try-completion, all-completions, and other basic
completion functions, which will then let your function do all
the work.
The completion function should accept three arguments:
nil if
none. Your function should call the predicate for each possible match,
and ignore the possible match if the predicate returns nil.
There are currently four methods, i.e. four flag values, one for each of the four different basic operations:
nil specifies try-completion. The completion function
should return the completion of the specified string, or t if the
string is a unique and exact match already, or nil if the string
matches no possibility.
If the string is an exact match for one possibility, but also matches
other longer possibilities, the function should return the string, not
t.
t specifies all-completions. The completion function
should return a list of all possible completions of the specified
string.
lambda specifies test-completion. The completion
function should return t if the specified string is an exact
match for some possibility; nil otherwise.
(boundaries . SUFFIX) specifies completion-boundaries.
The function should return a value of the form (boundaries
START . END) where START is the position of the beginning boundary in
in the string to complete, and END is the position of the end boundary
in SUFFIX.
It would be consistent and clean for completion functions to allow lambda expressions (lists that are functions) as well as function symbols as collection, but this is impossible. Lists as completion tables already have other meanings, and it would be unreliable to treat one differently just because it is also a possible function. So you must arrange for any function you wish to use for completion to be encapsulated in a symbol.
This function is a convenient way to write a function that can act as programmed completion function. The argument function should be a function that takes one argument, a string, and returns an alist of possible completions of it. You can think of
completion-table-dynamicas a transducer between that interface and the interface for programmed completion functions.
The value of this variable, if non-
nil, should be a function for “annotating” the entries in the ‘*Completions*’ buffer. The function should accept a single argument, the completion string for an entry. It should return an additional string to display next to that entry in the ‘*Completions*’ buffer, ornilif no additional string is to be displayed.The function can determine the collection used for the current completion via the variable
minibuffer-completion-table(see Completion Commands).
This section describes functions used to ask the user a yes-or-no
question. The function y-or-n-p can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. yes-or-no-p is suitable for
more momentous questions, since it requires three or four characters to
answer.
If either of these functions is called in a command that was invoked
using the mouse—more precisely, if last-nonmenu-event
(see Command Loop Info) is either nil or a list—then it
uses a dialog box or pop-up menu to ask the question. Otherwise, it
uses keyboard input. You can force use of the mouse or use of keyboard
input by binding last-nonmenu-event to a suitable value around
the call.
Strictly speaking, yes-or-no-p uses the minibuffer and
y-or-n-p does not; but it seems best to describe them together.
This function asks the user a question, expecting input in the echo area. It returns
tif the user types y,nilif the user types n. This function also accepts <SPC> to mean yes and <DEL> to mean no. It accepts C-] to mean “quit,” like C-g, because the question might look like a minibuffer and for that reason the user might try to use C-] to get out. The answer is a single character, with no <RET> needed to terminate it. Upper and lower case are equivalent.“Asking the question” means printing prompt in the echo area, followed by the string ‘(y or n) ’. If the input is not one of the expected answers (y, n, <SPC>, <DEL>, or something that quits), the function responds ‘Please answer y or n.’, and repeats the request.
This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see The Echo Area), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.
The answers and their meanings, even ‘y’ and ‘n’, are not hardwired. The keymap
query-replace-mapspecifies them. See Search and Replace.In the following example, the user first types q, which is invalid. At the next prompt the user types y.
(y-or-n-p "Do you need a lift? ") ;; After evaluation of the preceding expression, ;; the following prompt appears in the echo area: ---------- Echo area ---------- Do you need a lift? (y or n) ---------- Echo area ---------- ;; If the user then types q, the following appears: ---------- Echo area ---------- Please answer y or n. Do you need a lift? (y or n) ---------- Echo area ---------- ;; When the user types a valid answer, ;; it is displayed after the question: ---------- Echo area ---------- Do you need a lift? (y or n) y ---------- Echo area ----------We show successive lines of echo area messages, but only one actually appears on the screen at a time.
Like
y-or-n-p, except that if the user fails to answer within seconds seconds, this function stops waiting and returns default-value. It works by setting up a timer; see Timers. The argument seconds may be an integer or a floating point number.
This function asks the user a question, expecting input in the minibuffer. It returns
tif the user enters ‘yes’,nilif the user types ‘no’. The user must type <RET> to finalize the response. Upper and lower case are equivalent.
yes-or-no-pstarts by displaying prompt in the echo area, followed by ‘(yes or no) ’. The user must type one of the expected responses; otherwise, the function responds ‘Please answer yes or no.’, waits about two seconds and repeats the request.
yes-or-no-prequires more work from the user thany-or-n-pand is appropriate for more crucial decisions.Here is an example:
(yes-or-no-p "Do you really want to remove everything? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------If the user first types y <RET>, which is invalid because this function demands the entire word ‘yes’, it responds by displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
When you have a series of similar questions to ask, such as “Do you
want to save this buffer” for each buffer in turn, you should use
map-y-or-n-p to ask the collection of questions, rather than
asking each question individually. This gives the user certain
convenient facilities such as the ability to answer the whole series at
once.
This function asks the user a series of questions, reading a single-character answer in the echo area for each one.
The value of list specifies the objects to ask questions about. It should be either a list of objects or a generator function. If it is a function, it should expect no arguments, and should return either the next object to ask about, or
nilmeaning stop asking questions.The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:
(format prompter object)where object is the next object to ask about (as obtained from list).
If not a string, prompter should be a function of one argument (the next object to ask about) and should return the question text. If the value is a string, that is the question to ask the user. The function can also return
tmeaning do act on this object (and don't ask the user), ornilmeaning ignore this object (and don't ask the user).The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list.
If the argument help is given, it should be a list of this form:
(singular plural action)where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does.
If you don't specify help, the default is
("object" "objects" "act on").Each time a question is asked, the user may enter y, Y, or <SPC> to act on that object; n, N, or <DEL> to skip that object; ! to act on all following objects; <ESC> or q to exit (skip all following objects); . (period) to act on the current object and then exit; or C-h to get help. These are the same answers that
query-replaceaccepts. The keymapquery-replace-mapdefines their meaning formap-y-or-n-pas well as forquery-replace; see Search and Replace.You can use action-alist to specify additional possible answers and what they mean. It is an alist of elements of the form
(char function help), each of which defines one additional answer. In this element, char is a character (the answer); function is a function of one argument (an object from list); help is a string.When the user responds with char,
map-y-or-n-pcalls function. If it returns non-nil, the object is considered “acted upon,” andmap-y-or-n-padvances to the next object in list. If it returnsnil, the prompt is repeated for the same object.Normally,
map-y-or-n-pbindscursor-in-echo-areawhile prompting. But if no-cursor-in-echo-area is non-nil, it does not do that.If
map-y-or-n-pis called in a command that was invoked using the mouse—more precisely, iflast-nonmenu-event(see Command Loop Info) is eithernilor a list—then it uses a dialog box or pop-up menu to ask the question. In this case, it does not use keyboard input or the echo area. You can force use of the mouse or use of keyboard input by bindinglast-nonmenu-eventto a suitable value around the call.The return value of
map-y-or-n-pis the number of objects acted on.
To read a password to pass to another program, you can use the
function read-passwd.
This function reads a password, prompting with prompt. It does not echo the password as the user types it; instead, it echoes ‘.’ for each character in the password.
The optional argument confirm, if non-
nil, says to read the password twice and insist it must be the same both times. If it isn't the same, the user has to type it over and over until the last two times match.The optional argument default specifies the default password to return if the user enters empty input. If default is
nil, thenread-passwdreturns the null string in that case.
This section describes some commands meant for use in the minibuffer.
This command exits the active minibuffer. It is normally bound to keys in minibuffer local keymaps.
This command exits the active minibuffer after inserting the last character typed on the keyboard (found in
last-command-event; see Command Loop Info).
This command replaces the minibuffer contents with the value of the nth previous (older) history element.
This command replaces the minibuffer contents with the value of the nth more recent history element.
This command replaces the minibuffer contents with the value of the nth previous (older) history element that matches pattern (a regular expression).
This command replaces the minibuffer contents with the value of the nth next (newer) history element that matches pattern (a regular expression).
These functions access and select minibuffer windows and test whether they are active.
This function returns the currently active minibuffer window, or
nilif none is currently active.
This function returns the minibuffer window used for frame frame. If frame is
nil, that stands for the current frame. Note that the minibuffer window used by a frame need not be part of that frame—a frame that has no minibuffer of its own necessarily uses some other frame's minibuffer window.
This function specifies window as the minibuffer window to use. This affects where the minibuffer is displayed if you put text in it without invoking the usual minibuffer commands. It has no effect on the usual minibuffer input functions because they all start by choosing the minibuffer window according to the current frame.
This function returns non-
nilif window is a minibuffer window. window defaults to the selected window.
It is not correct to determine whether a given window is a minibuffer by
comparing it with the result of (minibuffer-window), because
there can be more than one minibuffer window if there is more than one
frame.
This function returns non-
nilif window, assumed to be a minibuffer window, is currently active.
These functions access the minibuffer prompt and contents.
This function returns the prompt string of the currently active minibuffer. If no minibuffer is active, it returns
nil.
This function returns the current position of the end of the minibuffer prompt, if a minibuffer is current. Otherwise, it returns the minimum valid buffer position.
This function returns the current display-width of the minibuffer prompt, if a minibuffer is current. Otherwise, it returns zero.
This function returns the editable contents of the minibuffer (that is, everything except the prompt) as a string, if a minibuffer is current. Otherwise, it returns the entire contents of the current buffer.
This is like
minibuffer-contents, except that it does not copy text properties, just the characters themselves. See Text Properties.
This is like
minibuffer-contents, except that it returns only the contents before point. That is the part that completion commands operate on. See Minibuffer Completion.
This function erases the editable contents of the minibuffer (that is, everything except the prompt), if a minibuffer is current. Otherwise, it erases the entire current buffer.
These functions and variables deal with recursive minibuffers (see Recursive Editing):
This function returns the current depth of activations of the minibuffer, a nonnegative integer. If no minibuffers are active, it returns zero.
If this variable is non-
nil, you can invoke commands (such asfind-file) that use minibuffers even while the minibuffer window is active. Such invocation produces a recursive editing level for a new minibuffer. The outer-level minibuffer is invisible while you are editing the inner one.If this variable is
nil, you cannot invoke minibuffer commands when the minibuffer window is active, not even if you switch to another window to do it.
If a command name has a property enable-recursive-minibuffers
that is non-nil, then the command can use the minibuffer to read
arguments even if it is invoked from the minibuffer. A command can
also achieve this by binding enable-recursive-minibuffers
to t in the interactive declaration (see Using Interactive).
The minibuffer command next-matching-history-element (normally
M-s in the minibuffer) does the latter.
This function returns non-
nilif buffer-or-name is a minibuffer. If buffer-or-name is omitted, it tests the current buffer.
This is a normal hook that is run whenever the minibuffer is entered. See Hooks.
This is a normal hook that is run whenever the minibuffer is exited. See Hooks.
The current value of this variable is used to rebind
help-formlocally inside the minibuffer (see Help Functions).
If the value of this variable is non-
nil, it should be a window object. When the functionscroll-other-windowis called in the minibuffer, it scrolls this window.
This function returns the window which was selected when the minibuffer was entered. If selected window is not a minibuffer window, it returns
nil.
This variable specifies the maximum height for resizing minibuffer windows. If a float, it specifies a fraction of the height of the frame. If an integer, it specifies a number of lines.
This function displays string temporarily at the end of the minibuffer text, for two seconds, or until the next input event arrives, whichever comes first. If args is non-
nil, the actual message is obtained by passing string and args throughformat. See Formatting Strings.
When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them.
The first thing the command loop must do is read a key sequence, which
is a sequence of events that translates into a command. It does this by
calling the function read-key-sequence. Your Lisp code can also
call this function (see Key Sequence Input). Lisp programs can also
do input at a lower level with read-event (see Reading One Event) or discard pending input with discard-input
(see Event Input Misc).
The key sequence is translated into a command through the currently
active keymaps. See Key Lookup, for information on how this is done.
The result should be a keyboard macro or an interactively callable
function. If the key is M-x, then it reads the name of another
command, which it then calls. This is done by the command
execute-extended-command (see Interactive Call).
Prior to executing the command, Emacs runs undo-boundary to
create an undo boundary. See Maintaining Undo.
To execute a command, Emacs first reads its arguments by calling
command-execute (see Interactive Call). For commands
written in Lisp, the interactive specification says how to read
the arguments. This may use the prefix argument (see Prefix Command Arguments) or may read with prompting in the minibuffer
(see Minibuffers). For example, the command find-file has
an interactive specification which says to read a file name
using the minibuffer. The function body of find-file does not
use the minibuffer, so if you call find-file as a function from
Lisp code, you must supply the file name string as an ordinary Lisp
function argument.
If the command is a string or vector (i.e., a keyboard macro) then
execute-kbd-macro is used to execute it. You can call this
function yourself (see Keyboard Macros).
To terminate the execution of a running command, type C-g. This character causes quitting (see Quitting).
The editor command loop runs this normal hook before each command. At that time,
this-commandcontains the command that is about to run, andlast-commanddescribes the previous command. See Command Loop Info.
The editor command loop runs this normal hook after each command (including commands terminated prematurely by quitting or by errors), and also when the command loop is first entered. At that time,
this-commandrefers to the command that just ran, andlast-commandrefers to the command before that.
Quitting is suppressed while running pre-command-hook and
post-command-hook. If an error happens while executing one of
these hooks, it terminates execution of the hook, and clears the hook
variable to nil so as to prevent an infinite loop of errors.
A request coming into the Emacs server (see Emacs Server) runs these two hooks just as a keyboard command does.
The special form interactive turns a Lisp function into a
command. The interactive form must be located at top-level in
the function body (usually as the first form in the body), or in the
interactive-form property of the function symbol. When the
interactive form is located in the function body, it does
nothing when actually executed. Its presence serves as a flag, which
tells the Emacs command loop that the function can be called
interactively. The argument of the interactive form controls
the reading of arguments for an interactive call.
interactive
This section describes how to write the interactive form that
makes a Lisp function an interactively-callable command, and how to
examine a command's interactive form.
This special form declares that a function is a command, and that it may therefore be called interactively (via M-x or by entering a key sequence bound to it). The argument arg-descriptor declares how to compute the arguments to the command when the command is called interactively.
A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and arg-descriptor has no effect.
The
interactiveform must be located at top-level in the function body, or in the function symbol'sinteractive-formproperty (see Symbol Plists). It has its effect because the command loop looks for it before calling the function (see Interactive Call). Once the function is called, all its body forms are executed; at this time, if theinteractiveform occurs within the body, the form simply returnsnilwithout even evaluating its argument.By convention, you should put the
interactiveform in the function body, as the first top-level form. If there is aninteractiveform in both theinteractive-formsymbol property and the function body, the former takes precedence. Theinteractive-formsymbol property can be used to add an interactive form to an existing function, or change how its arguments are processed interactively, without redefining the function.
There are three possibilities for the argument arg-descriptor:
nil; then the command is called with no
arguments. This leads quickly to an error if the command requires one
or more arguments.
(interactive "P\nbFrobnicate buffer: ")
The code letter ‘P’ sets the command's first argument to the raw command prefix (see Prefix Command Arguments). ‘bFrobnicate buffer: ’ prompts the user with ‘Frobnicate buffer: ’ to enter the name of an existing buffer, which becomes the second and final argument.
The prompt string can use ‘%’ to include previous argument values
(starting with the first argument) in the prompt. This is done using
format (see Formatting Strings). For example, here is how
you could read the name of an existing buffer followed by a new name to
give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
If ‘*’ appears at the beginning of the string, then an error is signaled if the buffer is read-only.
If ‘@’ appears at the beginning of the string, and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run.
If ‘^’ appears at the beginning of the string, and if the command
was invoked through shift-translation, set the mark and activate
the region temporarily, or extend an already active region, before the
command is run. If the command was invoked without shift-translation,
and the region is temporarily active, deactivate the region before the
command is run. Shift-translation is controlled on the user level by
shift-select-mode; see Shift Selection.
You can use ‘*’, ‘@’, and ^ together; the order does
not matter. Actual reading of arguments is controlled by the rest of
the prompt string (starting with the first character that is not
‘*’, ‘@’, or ‘^’).
Providing point or the mark as an argument value is also common, but if you do this and read input (whether using the minibuffer or not), be sure to get the integer values of point or the mark after reading. The current buffer may be receiving subprocess output; if subprocess output arrives while the command is waiting for input, it could relocate point and the mark.
Here's an example of what not to do:
(interactive
(list (region-beginning) (region-end)
(read-string "Foo: " nil 'my-history)))
Here's how to avoid the problem, by examining point and the mark after reading the keyboard input:
(interactive
(let ((string (read-string "Foo: " nil 'my-history)))
(list (region-beginning) (region-end) string)))
Warning: the argument values should not include any data
types that can't be printed and then read. Some facilities save
command-history in a file to be read in the subsequent
sessions; if a command's arguments contain a data type that prints
using ‘#<...>’ syntax, those facilities won't work.
There are, however, a few exceptions: it is ok to use a limited set of
expressions such as (point), (mark),
(region-beginning), and (region-end), because Emacs
recognizes them specially and puts the expression (rather than its
value) into the command history. To see whether the expression you
wrote is one of these exceptions, run the command, then examine
(car command-history).
This function returns the
interactiveform of function. If function is an interactively callable function (see Interactive Call), the value is the command'sinteractiveform(interactivespec), which specifies how to compute its arguments. Otherwise, the value isnil. If function is a symbol, its function definition is used.
interactiveThe code character descriptions below contain a number of key words, defined here as follows:
completing-read
(see Completion). ? displays a list of possible completions.
Even though the code letter doesn't use a prompt string, you must follow
it with a newline if it is not the last code character in the string.
Here are the code character descriptions for use with interactive:
fboundp). Existing,
Completion, Prompt.
commandp). Existing,
Completion, Prompt.
default-directory (see File Name Expansion).
Existing, Completion, Default, Prompt.
You can use ‘e’ more than once in a single command's interactive
specification. If the key sequence that invoked the command has
n events that are lists, the nth ‘e’ provides the
nth such event. Events that are not lists, such as function keys
and ASCII characters, do not count where ‘e’ is concerned.
default-directory. Existing, Completion, Default,
Prompt.
nil as
the argument's value. No I/O.
If ‘k’ reads a key sequence that ends with a down-event, it also reads and discards the following up-event. You can get access to that up-event with the ‘U’ code character.
This kind of input is used by commands such as describe-key and
global-set-key.
nil. Can be used after a ‘k’ or
‘K’ argument to get the up-event that was discarded (if any)
after ‘k’ or ‘K’ read a down-event. If no up-event has been
discarded, ‘U’ provides nil as the argument. No I/O.
user-variable-p). This reads the variable using
read-variable. See Definition of read-variable. Existing,
Completion, Prompt.
nil. See Coding Systems. Completion,
Existing, Prompt.
nil as the
argument value. Completion, Existing, Prompt.
interactive
Here are some examples of interactive:
(defun foo1 () ;foo1takes no arguments, (interactive) ; just moves forward two words. (forward-word 2)) ⇒ foo1 (defun foo2 (n) ;foo2takes one argument, (interactive "^p") ; which is the numeric prefix. ; undershift-select-mode, ; will activate or extend region. (forward-word (* 2 n))) ⇒ foo2 (defun foo3 (n) ;foo3takes one argument, (interactive "nCount:") ; which is read with the Minibuffer. (forward-word (* 2 n))) ⇒ foo3 (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) ⇒ three-b (three-b "*scratch*" "declarations.texi" "*mail*") ⇒ nil
After the command loop has translated a key sequence into a command,
it invokes that command using the function command-execute. If
the command is a function, command-execute calls
call-interactively, which reads the arguments and calls the
command. You can also call these functions yourself.
Returns
tif object is suitable for calling interactively; that is, if object is a command. Otherwise, returnsnil.Interactively-callable objects include strings and vectors (which are treated as keyboard macros), lambda expressions that contain a top-level
interactiveform (see Using Interactive), byte-code function objects made from such lambda expressions, autoload objects that are declared as interactive (non-nilfourth argument toautoload), and some primitive functions.A symbol satisfies
commandpif it has a non-nilinteractive-formproperty, or if its function definition satisfiescommandp. Keys and keymaps are not commands. Rather, they are used to look up commands (see Keymaps).If for-call-interactively is non-
nil, thencommandpreturnstonly for objects thatcall-interactivelycould call—thus, not for keyboard macros.See
documentationin Accessing Documentation, for a realistic example of usingcommandp.
This function calls the interactively callable function command, reading arguments according to its interactive calling specifications. It returns whatever command returns. An error is signaled if command is not a function or if it cannot be called interactively (i.e., is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands, because they are not functions. If command is a symbol, then
call-interactivelyuses its function definition.If record-flag is non-
nil, then this command and its arguments are unconditionally added to the listcommand-history. Otherwise, the command is added only if it uses the minibuffer to read an argument. See Command History.The argument keys, if given, should be a vector which specifies the sequence of events to supply if the command inquires which events were used to invoke it. If keys is omitted or
nil, the default is the return value ofthis-command-keys-vector. See Definition of this-command-keys-vector.
This function executes command. The argument command must satisfy the
commandppredicate; i.e., it must be an interactively callable function or a keyboard macro.A string or vector as command is executed with
execute-kbd-macro. A function is passed tocall-interactively, along with the optional record-flag and keys.A symbol is handled by using its function definition in its place. A symbol with an
autoloaddefinition counts as a command if it was declared to stand for an interactively callable function. Such a definition is handled by loading the specified library and then rechecking the definition of the symbol.The argument special, if given, means to ignore the prefix argument and not clear it. This is used for executing special events (see Special Events).
This function reads a command name from the minibuffer using
completing-read(see Completion). Then it usescommand-executeto call the specified command. Whatever that command returns becomes the value ofexecute-extended-command.If the command asks for a prefix argument, it receives the value prefix-argument. If
execute-extended-commandis called interactively, the current raw prefix argument is used for prefix-argument, and thus passed on to whatever command is run.
execute-extended-commandis the normal definition of M-x, so it uses the string ‘M-x ’ as a prompt. (It would be better to take the prompt from the events used to invokeexecute-extended-command, but that is painful to implement.) A description of the value of the prefix argument, if any, also becomes part of the prompt.(execute-extended-command 3) ---------- Buffer: Minibuffer ---------- 3 M-x forward-word RET ---------- Buffer: Minibuffer ---------- ⇒ t
Sometimes a command should display additional visual feedback (such
as an informative message in the echo area) for interactive calls
only. There are three ways to do this. The recommended way to test
whether the function was called using call-interactively is to
give it an optional argument print-message and use the
interactive spec to make it non-nil in interactive
calls. Here's an example:
(defun foo (&optional print-message)
(interactive "p")
(when print-message
(message "foo")))
We use "p" because the numeric prefix argument is never
nil. Defined in this way, the function does display the
message when called from a keyboard macro.
The above method with the additional argument is usually best,
because it allows callers to say “treat this call as interactive.”
But you can also do the job by testing called-interactively-p.
This function returns
twhen the calling function was called usingcall-interactively.The argument kind should be either the symbol
interactiveor the symbolany. If it isinteractive, thencalled-interactively-preturnstonly if the call was made directly by the user—e.g., if the user typed a key sequence bound to the calling function, but not if the user ran a keyboard macro that called the function (see Keyboard Macros). If kind isany,called-interactively-preturnstfor any kind of interactive call, including keyboard macros.If in doubt, use
any; the only known proper use ofinteractiveis if you need to decide whether to display a helpful message while a function is running.A function is never considered to be called interactively if it was called via Lisp evaluation (or with
applyorfuncall).
Here is an example of using called-interactively-p:
(defun foo ()
(interactive)
(when (called-interactively-p 'any)
(message "Interactive!")
'foo-called-interactively))
;; Type M-x foo.
-| Interactive!
(foo)
⇒ nil
Here is another example that contrasts direct and indirect calls to
called-interactively-p.
(defun bar ()
(interactive)
(message "%s" (list (foo) (called-interactively-p 'any))))
;; Type M-x bar.
-| (nil t)
The editor command loop sets several Lisp variables to keep status
records for itself and for commands that are run. With the exception of
this-command and last-command it's generally a bad idea to
change any of these variables in a Lisp program.
This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed.
The value is copied from
this-commandwhen a command returns to the command loop, except when the command has specified a prefix argument for the following command.This variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
This variable is set up by Emacs just like
last-command, but never altered by Lisp programs.
This variable stores the most recently executed command that was not part of an input event. This is the command
repeatwill try to repeat, See Repeating.
This variable records the name of the command now being executed by the editor command loop. Like
last-command, it is normally a symbol with a function definition.The command loop sets this variable just before running a command, and copies its value into
last-commandwhen the command finishes (unless the command specified a prefix argument for the following command).Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set
this-commandtokill-regionso that any kill commands immediately following will know to append the killed text to the previous kill.
If you do not want a particular command to be recognized as the previous
command in the case where it got an error, you must code that command to
prevent this. One way is to set this-command to t at the
beginning of the command, and set this-command back to its proper
value at the end, like this:
(defun foo (args...)
(interactive ...)
(let ((old-this-command this-command))
(setq this-command t)
...do the work...
(setq this-command old-this-command)))
We do not bind this-command with let because that would
restore the old value in case of error—a feature of let which
in this case does precisely what we want to avoid.
This has the same value as
this-commandexcept when command remapping occurs (see Remapping Commands). In that case,this-commandgives the command actually run (the result of remapping), andthis-original-commandgives the command that was specified to run but remapped into another command.
This function returns a string or vector containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command. Any events read by the command using
read-eventwithout a timeout get tacked on to the end.However, if the command has called
read-key-sequence, it returns the last read key sequence. See Key Sequence Input. The value is a string if all events in the sequence were characters that fit in a string. See Input Events.(this-command-keys) ;; Now use C-u C-x C-e to evaluate that. ⇒ "^U^X^E"
Like
this-command-keys, except that it always returns the events in a vector, so you don't need to deal with the complexities of storing input events in a string (see Strings of Events).
This function empties out the table of events for
this-command-keysto return. Unless keep-record is non-nil, it also empties the records that the functionrecent-keys(see Recording Input) will subsequently return. This is useful after reading a password, to prevent the password from echoing inadvertently as part of the next command in certain cases.
This variable holds the last input event read as part of a key sequence, not counting events resulting from mouse menus.
One use of this variable is for telling
x-popup-menuwhere to pop up a menu. It is also used internally byy-or-n-p(see Yes-or-No Queries).
This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in
self-insert-command, which uses it to decide which character to insert.last-command-event ;; Now use C-u C-x C-e to evaluate that. ⇒ 5The value is 5 because that is the ASCII code for C-e.
The alias
last-command-charis obsolete.
This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. See Input Focus.
If the last event came from a keyboard macro, the value is
macro.
It is not easy to display a value of point in the middle of a
sequence of text that has the display, composition or
intangible property, or is invisible. Therefore, after a
command finishes and returns to the command loop, if point is within
such a sequence, the command loop normally moves point to the edge of
the sequence.
A command can inhibit this feature by setting the variable
disable-point-adjustment:
If this variable is non-
nilwhen a command returns to the command loop, then the command loop does not check for those text properties, and does not move point out of sequences that have them.The command loop sets this variable to
nilbefore each command, so if a command sets it, the effect applies only to that command.
If you set this variable to a non-
nilvalue, the feature of moving point out of these sequences is completely turned off.
The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity. The events for keyboard activity are characters or symbols; mouse events are always lists. This section describes the representation and meaning of input events in detail.
This function returns non-
nilif object is an input event or event type.Note that any symbol might be used as an event or an event type.
eventpcannot distinguish whether a symbol is intended by Lisp code to be used as an event. Instead, it distinguishes whether the symbol has actually been used in an event that has been read as input in the current Emacs session. If a symbol has not yet been so used,eventpreturnsnil.
There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. The event type of a character event is the character itself (an integer); see Classifying Events.
An input character event consists of a basic code between 0 and 524287, plus any or all of these modifier bits:
ascii control characters such as C-a have special basic codes of their own, so Emacs needs no special bit to indicate them. Thus, the code for C-a is just 1.
But if you type a control combination not in ASCII, such as
% with the control key, the numeric value you get is the code
for % plus
2**26
(assuming the terminal supports non-ASCII
control characters).
For letters, the basic code itself indicates upper versus lower case; for digits and punctuation, the shift key selects an entirely different character with a different basic code. In order to keep within the ASCII character set whenever possible, Emacs avoids using the 2**25 bit for those characters.
However, ASCII provides no way to distinguish C-A from
C-a, so Emacs uses the
2**25
bit in C-A and not in
C-a.
It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
event-modifiers (see Classifying Events). When making key
bindings, you can use the read syntax for characters with modifier bits
(‘\C-’, ‘\M-’, and so on). For making key bindings with
define-key, you can use lists such as (control hyper ?x) to
specify the characters (see Changing Key Bindings). The function
event-convert-list converts such a list into an event type
(see Classifying Events).
Most keyboards also have function keys—keys that have names or
symbols that are not characters. Function keys are represented in Emacs
Lisp as symbols; the symbol's name is the function key's label, in lower
case. For example, pressing a key labeled <F1> places the symbol
f1 in the input stream.
The event type of a function key event is the event symbol itself. See Classifying Events.
Here are a few special cases in the symbol-naming convention for function keys:
backspace, tab, newline, return, deleteIn ASCII, C-i and <TAB> are the same character. If the
terminal can distinguish between them, Emacs conveys the distinction to
Lisp programs by representing the former as the integer 9, and the
latter as the symbol tab.
Most of the time, it's not useful to distinguish the two. So normally
local-function-key-map (see Translation Keymaps) is set up
to map tab into 9. Thus, a key binding for character code 9
(the character C-i) also applies to tab. Likewise for
the other symbols in this group. The function read-char
likewise converts these events into characters.
In ASCII, <BS> is really C-h. But backspace
converts into the character code 127 (<DEL>), not into code 8
(<BS>). This is what most users prefer.
left, up, right, downkp-add, kp-decimal, kp-divide, ...kp-0, kp-1, ...kp-f1, kp-f2, kp-f3, kp-f4kp-home, kp-left, kp-up, kp-right, kp-downhome, left, ...
kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-deleteYou can use the modifier keys <ALT>, <CTRL>, <HYPER>, <META>, <SHIFT>, and <SUPER> with function keys. The way to represent them is with prefixes in the symbol name:
Thus, the symbol for the key <F3> with <META> held down is
M-f3. When you use more than one prefix, we recommend you
write them in alphabetical order; but the order does not matter in
arguments to the key-binding lookup and modification functions.
Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The car of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (see Repeat Events). The rest of the list elements give position and time information.
For key lookup, only the event type matters: two events of the same type necessarily run the same command. The command can access the full values of these events using the ‘e’ interactive code. See Interactive Codes.
A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer—that is entirely under the control of the command binding of the key sequence.
When the user presses a mouse button and releases it at the same location, that generates a click event. All mouse click event share the same format:
(event-type position click-count)
mouse-1, mouse-2, ..., where the
buttons are numbered left to right.
You can also use prefixes ‘A-’, ‘C-’, ‘H-’, ‘M-’, ‘S-’ and ‘s-’ for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys.
This symbol also serves as the event type of the event. Key bindings
describe events by their types; thus, if there is a key binding for
mouse-1, that binding would apply to all events whose
event-type is mouse-1.
For mouse click events in the text area, mode line, header line, or in the marginal areas, position has this form:
(window pos-or-area (x . y) timestamp
object text-pos (col . row)
image (dx . dy) (width . height))
mode-line,
header-line, vertical-line, left-margin,
right-margin, left-fringe, or right-fringe.
In one special case, pos-or-area is a list containing a symbol (one
of the symbols listed above) instead of just the symbol. This happens
after the imaginary prefix keys for the event are inserted into the
input stream. See Key Sequence Input.
(0 . 0).
For the mode or header line, y does not have meaningful data.
For the vertical line, x does not have meaningful data.
nil if there is no string property, or it has the form
(string . string-pos) when there is a string-type text
property at the click position.
nil if there is no image at the position clicked on, or it is
an image object as returned by find-image if click was in an image.
(0 . 0). If
object is nil, the coordinates are relative to the top
left corner of the character glyph clicked on.
nil, those of the character glyph clicked on.
For mouse clicks on a scroll-bar, position has this form:
(window area (portion . whole) timestamp part)
vertical-scroll-bar or horizontal-scroll-bar.
above-handle, handle, below-handle,
up, down, top, bottom, and end-scroll.
With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this:
(event-type
(window1 START-POSITION)
(window2 END-POSITION))
For a drag event, the name of the symbol event-type contains the
prefix ‘drag-’. For example, dragging the mouse with button 2
held down generates a drag-mouse-2 event. The second and third
elements of the event give the starting and ending position of the
drag. They have the same form as position in a click event
(see Click Events) that is not on the scroll bar part of the
window. You can access the second element of any mouse event in the
same way, with no need to distinguish drag events from others.
The ‘drag-’ prefix follows the modifier key prefixes such as ‘C-’ and ‘M-’.
If read-key-sequence receives a drag event that has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position. This means that you don't have to distinguish between click
and drag events unless you want to.
Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need to handle button-down events.9 These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (see Click Events), except that the event-type symbol name contains the prefix ‘down-’. The ‘down-’ prefix follows modifier key prefixes such as ‘C-’ and ‘M-’.
The function read-key-sequence ignores any button-down events
that don't have command bindings; therefore, the Emacs command loop
ignores them too. This means that you need not worry about defining
button-down events unless you want them to do something. The usual
reason to define a button-down event is so that you can track mouse
motion (by reading motion events) until the button is released.
See Motion Events.
If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special repeat mouse events for the second and subsequent presses.
The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events).
The event type of a double-click event contains the prefix
‘double-’. Thus, a double click on the second mouse button with
<meta> held down comes to the Lisp program as
M-double-mouse-2. If a double-click event has no binding, the
binding of the corresponding ordinary click event is used to execute
it. Thus, you need not pay attention to the double click feature
unless you really want to.
When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click.
This is convenient, if the meaning of a double click somehow “builds on” the meaning of a single click—which is recommended user interface design practice for double clicks.
If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains ‘double-drag’ instead of just ‘drag’. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag.
Before the double-click or double-drag event, Emacs generates a double-down event when the user presses the button down for the second time. Its event type contains ‘double-down’ instead of just ‘down’. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored.
To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event.
If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain ‘triple’ instead of ‘double’. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event.
If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc. events. However, you can look at the event list to find out precisely how many times the button was pressed.
This function returns the number of consecutive button presses that led up to event. If event is a double-down, double-click or double-drag event, the value is 2. If event is a triple event, the value is 3 or greater. If event is an ordinary mouse event (not a repeat event), the value is 1.
To generate repeat events, successive mouse button presses must be at approximately the same screen position. The value of
double-click-fuzzspecifies the maximum number of pixels the mouse may be moved (horizontally or vertically) between two successive clicks to make a double-click.This variable is also the threshold for motion of the mouse to count as a drag.
To generate repeat events, the number of milliseconds between successive button presses must be less than the value of
double-click-time. Settingdouble-click-timetonildisables multi-click detection entirely. Setting it totremoves the time limit; Emacs then detects multi-clicks by position only.
Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this:
(mouse-movement POSITION)
The second element of the list describes the current position of the mouse, just as in a click event (see Click Events).
The special form track-mouse enables generation of motion events
within its body. Outside of track-mouse forms, Emacs does not
generate events for mere motion of the mouse, and these events do not
appear. See Mouse Tracking.
Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See Input Focus.
Focus events are represented in Lisp as lists that look like this:
(switch-frame new-frame)
where new-frame is the frame switched to.
Some X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Usually, there is no need for a Lisp program to know about the focus change until some other kind of input arrives. Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event.
A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it.
A few other event types represent occurrences within the system.
(delete-frame (frame))The standard definition of the delete-frame event is to delete frame.
(iconify-frame (frame))ignore; since the
frame has already been iconified, Emacs has no work to do. The purpose
of this event type is so that you can keep track of such events if you
want to.
(make-frame-visible (frame))ignore; since the
frame has already been made visible, Emacs has no work to do.
(wheel-up position)(wheel-down position)The element position is a list describing the position of the event, in the same format as used in a mouse-click event.
This kind of event is generated only on some kinds of systems. On some
systems, mouse-4 and mouse-5 are used instead. For
portable code, use the variables mouse-wheel-up-event and
mouse-wheel-down-event defined in mwheel.el to determine
what event types to expect for the mouse wheel.
(drag-n-drop position files)The element position is a list describing the position of the event, in the same format as used in a mouse-click event, and files is the list of file names that were dragged and dropped. The usual way to handle this event is by visiting these files.
This kind of event is generated, at present, only on some kinds of systems.
help-echohelp-echo text property.
The generated event has this form:
(help-echo frame help window object pos)
The precise meaning of the event parameters and the way these parameters are used to display the help-echo text are described in Text help-echo.
sigusr1sigusr2SIGUSR1 and SIGUSR2. They contain no
additional data because signals do not carry additional information.
To catch a user signal, bind the corresponding event to an interactive
command in the special-event-map (see Active Keymaps).
The command is called with no arguments, and the specific signal event is
available in last-input-event. For example:
(defun sigusr-handler ()
(interactive)
(message "Caught signal %S" last-input-event))
(define-key special-event-map [sigusr1] 'sigusr-handler)
To test the signal handler, you can make Emacs send a signal to itself:
(signal-process (emacs-pid) 'sigusr1)
If one of these events arrives in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it.
If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this:
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
(mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here:
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
(#<window 18 on NEWS> 3510 (0 . 28) -729648))
While holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces a pair of events like these:
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
-453816))
To handle a SIGUSR1 signal, define an interactive function, and
bind it to the signal usr1 event sequence:
(defun usr1-handler ()
(interactive)
(message "Got USR1 signal"))
(global-set-key [signal usr1] 'usr1-handler)
Every event has an event type, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the car of the list. Thus, the event type is always a symbol or a character.
Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act.
Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the <META> key, regardless of which other key or mouse button was used.
The functions event-modifiers and event-basic-type are
provided to get such information conveniently.
This function returns a list of the modifiers that event has. The modifiers are symbols; they include
shift,control,meta,alt,hyperandsuper. In addition, the modifiers list of a mouse event symbol always contains one ofclick,drag, anddown. For double or triple events, it also containsdoubleortriple.The argument event may be an entire event object, or just an event type. If event is a symbol that has never been used in an event that has been read as input in the current Emacs session, then
event-modifierscan returnnil, even when event actually has modifiers.Here are some examples:
(event-modifiers ?a) ⇒ nil (event-modifiers ?A) ⇒ (shift) (event-modifiers ?\C-a) ⇒ (control) (event-modifiers ?\C-%) ⇒ (control) (event-modifiers ?\C-\S-a) ⇒ (control shift) (event-modifiers 'f5) ⇒ nil (event-modifiers 's-f5) ⇒ (super) (event-modifiers 'M-S-f5) ⇒ (meta shift) (event-modifiers 'mouse-1) ⇒ (click) (event-modifiers 'down-mouse-1) ⇒ (down)The modifiers list for a click event explicitly contains
click, but the event symbol name itself does not contain ‘click’.
This function returns the key or mouse button that event describes, with all modifiers removed. The event argument is as in
event-modifiers. For example:(event-basic-type ?a) ⇒ 97 (event-basic-type ?A) ⇒ 97 (event-basic-type ?\C-a) ⇒ 97 (event-basic-type ?\C-\S-a) ⇒ 97 (event-basic-type 'f5) ⇒ f5 (event-basic-type 's-f5) ⇒ f5 (event-basic-type 'M-S-f5) ⇒ f5 (event-basic-type 'down-mouse-1) ⇒ mouse-1
This function returns non-
nilif object is a mouse movement event.
This function converts a list of modifier names and a basic event type to an event type which specifies all of them. The basic event type must be the last element of the list. For example,
(event-convert-list '(control ?a)) ⇒ 1 (event-convert-list '(control meta ?a)) ⇒ -134217727 (event-convert-list '(control super f1)) ⇒ C-s-f1
This section describes convenient functions for accessing the data in a mouse button or motion event.
These two functions return the starting or ending position of a mouse-button event, as a list of this form:
(window pos-or-area (x . y) timestamp
object text-pos (col . row)
image (dx . dy) (width . height))
This returns the starting position of event.
If event is a click or button-down event, this returns the location of the event. If event is a drag event, this returns the drag's starting position.
This returns the ending position of event.
If event is a drag event, this returns the position where the user released the mouse button. If event is a click or button-down event, the value is actually the starting position, which is the only position such events have.
These functions take a position list as described above, and return various parts of it.
Return the window area recorded in position. It returns
nilwhen the event occurred in the text area of the window; otherwise, it is a symbol identifying the area in which the event occurred.
Return the buffer position in position. When the event occurred in the text area of the window, in a marginal area, or on a fringe, this is an integer specifying a buffer position. Otherwise, the value is undefined.
Return the pixel-based x and y coordinates in position, as a cons cell
(x.y). These coordinates are relative to the window given byposn-window.This example shows how to convert these window-relative coordinates into frame-relative coordinates:
(defun frame-relative-coordinates (position) "Return frame-relative coordinates from POSITION." (let* ((x-y (posn-x-y position)) (window (posn-window position)) (edges (window-inside-pixel-edges window))) (cons (+ (car x-y) (car edges)) (+ (cdr x-y) (cadr edges)))))
This function returns a cons cell
(col.row), containing the estimated column and row corresponding to buffer position position. The return value is given in units of the frame's default character width and height, as computed from the x and y values corresponding to position. (So, if the actual characters have non-default sizes, the actual row and column may differ from these computed values.)Note that row is counted from the top of the text area. If the window possesses a header line (see Header Lines), it is not counted as the first line.
Return the actual row and column in position, as a cons cell
(col.row). The values are the actual row number in the window, and the actual character number in that row. It returnsnilif position does not include actual positions values. You can useposn-col-rowto get approximate values.
Return the string object in position, either
nil, or a cons cell(string.string-pos).
Return the image object in position, either
nil, or an image(image ...).
Return the image or string object in position, either
nil, an image(image ...), or a cons cell(string.string-pos).
Return the pixel-based x and y coordinates relative to the upper left corner of the object in position as a cons cell
(dx.dy). If the position is a buffer position, return the relative position in the character at that position.
Return the pixel width and height of the object in position as a cons cell
(width.height). If the position is a buffer position, return the size of the character at that position.
Return the timestamp in position. This is the time at which the event occurred, in milliseconds.
These functions compute a position list given particular buffer position or screen position. You can access the data in this position list with the functions described above.
This function returns a position list for position pos in window. pos defaults to point in window; window defaults to the selected window.
posn-at-pointreturnsnilif pos is not visible in window.
This function returns position information corresponding to pixel coordinates x and y in a specified frame or window, frame-or-window, which defaults to the selected window. The coordinates x and y are relative to the frame or window used. If whole is
nil, the coordinates are relative to the window text area, otherwise they are relative to the entire window area including scroll bars, margins and fringes.
These functions are useful for decoding scroll bar events.
This function returns the fractional vertical position of a scroll bar event within the scroll bar. The value is a cons cell
(portion.whole)containing two integers whose ratio is the fractional position.
This function multiplies (in effect) ratio by total, rounding the result to an integer. The argument ratio is not a number, but rather a pair
(num.denom)—typically a value returned byscroll-bar-event-ratio.This function is handy for scaling a position on a scroll bar into a buffer position. Here's how to do that:
(+ (point-min) (scroll-bar-scale (posn-x-y (event-start event)) (- (point-max) (point-min))))Recall that scroll bar events have two integers forming a ratio, in place of a pair of x and y coordinates.
In most of the places where strings are used, we conceptualize the string as containing text characters—the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. However, storing keyboard characters in a string is a complex matter, for reasons of historical compatibility, and it is not always possible.
We recommend that new programs avoid dealing with these complexities by not storing keyboard events in strings. Here is how to do that:
lookup-key and
define-key. For example, you can use
read-key-sequence-vector instead of read-key-sequence, and
this-command-keys-vector instead of this-command-keys.
define-key.
listify-key-sequence (see Event Input Misc)
first, to convert it to a list.
The complexities stem from the modifier bits that keyboard input characters can include. Aside from the Meta modifier, none of these modifier bits can be included in a string, and the Meta modifier is allowed only in special cases.
The earliest GNU Emacs versions represented meta characters as codes
in the range of 128 to 255. At that time, the basic character codes
ranged from 0 to 127, so all keyboard character codes did fit in a
string. Many Lisp programs used ‘\M-’ in string constants to stand
for meta characters, especially in arguments to define-key and
similar functions, and key sequences and sequences of events were always
represented as strings.
When we added support for larger basic character codes beyond 127, and additional modifier bits, we had to change the representation of meta characters. Now the flag that represents the Meta modifier in a character is 2**27 and such numbers cannot be included in a string.
To support programs with ‘\M-’ in string constants, there are special rules for including certain meta characters in a string. Here are the rules for interpreting a string as a sequence of input characters:
Functions such as read-key-sequence that construct strings of
keyboard input characters follow these rules: they construct vectors
instead of strings, when the events won't fit in a string.
When you use the read syntax ‘\M-’ in a string, it produces a code in the range of 128 to 255—the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings.
However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section.
The editor command loop reads key sequences using the function
read-key-sequence, which uses read-event. These and other
functions for event input are also available for use in Lisp programs.
See also momentary-string-display in Temporary Displays,
and sit-for in Waiting. See Terminal Input, for
functions and variables for controlling terminal input modes and
debugging terminal input.
For higher-level input facilities, see Minibuffers.
The command loop reads input a key sequence at a time, by calling
read-key-sequence. Lisp programs can also call this function;
for example, describe-key uses it to read the key to describe.
This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a complete key sequence; that is, enough to specify a non-prefix command using the currently active keymaps. (Remember that a key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer.)
If the events are all characters and all can fit in a string, then
read-key-sequencereturns a string (see Strings of Events). Otherwise, it returns a vector, since a vector can hold all kinds of events—characters, symbols, and lists. The elements of the string or vector are the events in the key sequence.Reading a key sequence includes translating the events in various ways. See Translation Keymaps.
The argument prompt is either a string to be displayed in the echo area as a prompt, or
nil, meaning not to display a prompt. The argument continue-echo, if non-nil, means to echo this key as a continuation of the previous key.Normally any upper case event is converted to lower case if the original event is undefined and the lower case equivalent is defined. The argument dont-downcase-last, if non-
nil, means do not convert the last event to lower case. This is appropriate for reading a key sequence to be defined.The argument switch-frame-ok, if non-
nil, means that this function should process aswitch-frameevent if the user switches frames before typing anything. If the user switches frames in the middle of a key sequence, or at the start of the sequence but switch-frame-ok isnil, then the event will be put off until after the current key sequence.The argument command-loop, if non-
nil, means that this key sequence is being read by something that will read commands one after another. It should benilif the caller will read just one key sequence.In the following example, Emacs displays the prompt ‘?’ in the echo area, and then the user types C-x C-f.
(read-key-sequence "?") ---------- Echo Area ---------- ?C-x C-f ---------- Echo Area ---------- ⇒ "^X^F"The function
read-key-sequencesuppresses quitting: C-g typed while reading with this function works like any other character, and does not setquit-flag. See Quitting.
This is like
read-key-sequenceexcept that it always returns the key sequence as a vector, never as a string. See Strings of Events.
If an input character is upper-case (or has the shift modifier) and
has no key binding, but its lower-case equivalent has one, then
read-key-sequence converts the character to lower case. Note
that lookup-key does not perform case conversion in this way.
When reading input results in such a shift-translation, Emacs
sets the variable this-command-keys-shift-translated to a
non-nil value. Lisp programs can examine this variable if they
need to modify their behavior when invoked by shift-translated keys.
For example, the function handle-shift-selection examines the
value of this variable to determine how to activate or deactivate the
region (see handle-shift-selection).
The function read-key-sequence also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special—it is the
same symbol that would normally represent that combination of mouse
button and modifier keys. The information about the window part is kept
elsewhere in the event—in the coordinates. But
read-key-sequence translates this information into imaginary
“prefix keys,” all of which are symbols: header-line,
horizontal-scroll-bar, menu-bar, mode-line,
vertical-line, and vertical-scroll-bar. You can define
meanings for mouse clicks in special window parts by defining key
sequences using these imaginary prefix keys.
For example, if you call read-key-sequence and then click the
mouse on the window's mode line, you get two events, like this:
(read-key-sequence "Click on the mode line: ")
⇒ [mode-line
(mouse-1
(#<window 6 on NEWS> mode-line
(40 . 63) 5959987))]
This variable's value is the number of key sequences processed so far in this Emacs session. This includes key sequences read from the terminal and key sequences read from keyboard macros being executed.
The lowest level functions for command input are read-event,
read-char, and read-char-exclusive.
This function reads and returns the next event of command input, waiting if necessary until an event is available. Events can come directly from the user or from a keyboard macro.
If the optional argument prompt is non-
nil, it should be a string to display in the echo area as a prompt. Otherwise,read-eventdoes not display any message to indicate it is waiting for input; instead, it prompts by echoing: it displays descriptions of the events that led to or were read by the current command. See The Echo Area.If inherit-input-method is non-
nil, then the current input method (if any) is employed to make it possible to enter a non-ASCII character. Otherwise, input method handling is disabled for reading this event.If
cursor-in-echo-areais non-nil, thenread-eventmoves the cursor temporarily to the echo area, to the end of any message displayed there. Otherwiseread-eventdoes not move the cursor.If seconds is non-
nil, it should be a number specifying the maximum time to wait for input, in seconds. If no input arrives within that time,read-eventstops waiting and returnsnil. A floating-point value for seconds means to wait for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down. If seconds isnil,read-eventwaits as long as necessary for input to arrive.If seconds is
nil, Emacs is considered idle while waiting for user input to arrive. Idle timers—those created withrun-with-idle-timer(see Idle Timers)—can run during this period. However, if seconds is non-nil, the state of idleness remains unchanged. If Emacs is non-idle whenread-eventis called, it remains non-idle throughout the operation ofread-event; if Emacs is idle (which can happen if the call happens inside an idle timer), it remains idle.If
read-eventgets an event that is defined as a help character, then in some casesread-eventprocesses the event directly without returning. See Help Functions. Certain other events, called special events, are also processed directly withinread-event(see Special Events).Here is what happens if you call
read-eventand then press the right-arrow function key:(read-event) ⇒ right
This function reads and returns a character of command input. If the user generates an event which is not a character (i.e. a mouse click or function key event),
read-charsignals an error. The arguments work as inread-event.In the first example, the user types the character 1 (ASCII code 49). The second example shows a keyboard macro definition that calls
read-charfrom the minibuffer usingeval-expression.read-charreads the keyboard macro's very next character, which is 1. Theneval-expressiondisplays its return value in the echo area.(read-char) ⇒ 49 ;; We assume here you use M-: to evaluate this. (symbol-function 'foo) ⇒ "^[:(read-char)^M1" (execute-kbd-macro 'foo) -| 49 ⇒ nil
This function reads and returns a character of command input. If the user generates an event which is not a character,
read-char-exclusiveignores it and reads another event, until it gets a character. The arguments work as inread-event.
None of the above functions suppress quitting.
This variable holds the total number of input events received so far from the terminal—not counting those generated by keyboard macros.
We emphasize that, unlike read-key-sequence, the functions
read-event, read-char, and read-char-exclusive do
not perform the translations described in Translation Keymaps.
If you wish to read a single key taking these translations into
account, use the function read-key:
This function reads a single key. It is “intermediate” between
read-key-sequenceandread-event. Unlike the former, it reads a single key, not a key sequence. Unlike the latter, it does not return a raw event, but decodes and translates the user input according toinput-decode-map,local-function-key-map, andkey-translation-map(see Translation Keymaps).The argument prompt is either a string to be displayed in the echo area as a prompt, or
nil, meaning not to display a prompt.
Emacs modifies every event it reads according to
extra-keyboard-modifiers, then translates it through
keyboard-translate-table (if applicable), before returning it
from read-event.
This variable lets Lisp programs “press” the modifier keys on the keyboard. The value is a character. Only the modifiers of the character matter. Each time the user types a keyboard key, it is altered as if those modifier keys were held down. For instance, if you bind
extra-keyboard-modifiersto?\C-\M-a, then all keyboard input characters typed during the scope of the binding will have the control and meta modifiers applied to them. The character?\C-@, equivalent to the integer 0, does not count as a control character for this purpose, but as a character with no modifiers. Thus, settingextra-keyboard-modifiersto zero cancels any modification.When using a window system, the program can “press” any of the modifier keys in this way. Otherwise, only the <CTL> and <META> keys can be virtually pressed.
Note that this variable applies only to events that really come from the keyboard, and has no effect on mouse events or any other events.
This terminal-local variable is the translate table for keyboard characters. It lets you reshuffle the keys on the keyboard without changing any command bindings. Its value is normally a char-table, or else
nil. (It can also be a string or vector, but this is considered obsolete.)If
keyboard-translate-tableis a char-table (see Char-Tables), then each character read from the keyboard is looked up in this char-table. If the value found there is non-nil, then it is used instead of the actual input character.Note that this translation is the first thing that happens to a character after it is read from the terminal. Record-keeping features such as
recent-keysand dribble files record the characters after translation.Note also that this translation is done before the characters are supplied to input methods (see Input Methods). Use
translation-table-for-input(see Translation of Characters), if you want to translate characters after input methods operate.
This function modifies
keyboard-translate-tableto translate character code from into character code to. It creates the keyboard translate table if necessary.
Here's an example of using the keyboard-translate-table to
make C-x, C-c and C-v perform the cut, copy and paste
operations:
(keyboard-translate ?\C-x 'control-x)
(keyboard-translate ?\C-c 'control-c)
(keyboard-translate ?\C-v 'control-v)
(global-set-key [control-x] 'kill-region)
(global-set-key [control-c] 'kill-ring-save)
(global-set-key [control-v] 'yank)
On a graphical terminal that supports extended ASCII input, you can still get the standard Emacs meanings of one of those characters by typing it with the shift key. That makes it a different character as far as keyboard translation is concerned, but it has the same usual meaning.
See Translation Keymaps, for mechanisms that translate event sequences
at the level of read-key-sequence.
The event-reading functions invoke the current input method, if any
(see Input Methods). If the value of input-method-function
is non-nil, it should be a function; when read-event reads
a printing character (including <SPC>) with no modifier bits, it
calls that function, passing the character as an argument.
If this is non-
nil, its value specifies the current input method function.Warning: don't bind this variable with
let. It is often buffer-local, and if you bind it around reading input (which is exactly when you would bind it), switching buffers asynchronously while Emacs is waiting will cause the value to be restored in the wrong buffer.
The input method function should return a list of events which should
be used as input. (If the list is nil, that means there is no
input, so read-event waits for another event.) These events are
processed before the events in unread-command-events
(see Event Input Misc). Events
returned by the input method function are not passed to the input method
function again, even if they are printing characters with no modifier
bits.
If the input method function calls read-event or
read-key-sequence, it should bind input-method-function to
nil first, to prevent recursion.
The input method function is not called when reading the second and
subsequent events of a key sequence. Thus, these characters are not
subject to input method processing. The input method function should
test the values of overriding-local-map and
overriding-terminal-local-map; if either of these variables is
non-nil, the input method should put its argument into a list and
return that list with no further processing.
You can use the function read-quoted-char to ask the user to
specify a character, and allow the user to specify a control or meta
character conveniently, either literally or as an octal character code.
The command quoted-insert uses this function.
This function is like
read-char, except that if the first character read is an octal digit (0-7), it reads any number of octal digits (but stopping if a non-octal digit is found), and returns the character represented by that numeric character code. If the character that terminates the sequence of octal digits is <RET>, it is discarded. Any other terminating character is used as input after this function returns.Quitting is suppressed when the first character is read, so that the user can enter a C-g. See Quitting.
If prompt is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single ‘-’.
In the following example, the user types in the octal number 177 (which is 127 in decimal).
(read-quoted-char "What character") ---------- Echo Area ---------- What character 1 7 7- ---------- Echo Area ---------- ⇒ 127
This section describes how to “peek ahead” at events without using
them up, how to check for pending input, and how to discard pending
input. See also the function read-passwd (see Reading a Password).
This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list, and removed one by one as they are used.
The variable is needed because in some cases a function reads an event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input.
For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally.
The reliable and easy way to extract events from a key sequence so as to put them in
unread-command-eventsis to uselistify-key-sequence(see Strings of Events).Normally you add events to the front of this list, so that the events most recently unread will be reread first.
Events read from this list are not normally added to the current command's key sequence (as returned by e.g.
this-command-keys), as the events will already have been added once as they were read for the first time. An element of the form(t .event)forces event to be added to the current command's key sequence.
This function converts the string or vector key to a list of individual events, which you can put in
unread-command-events.
This variable holds a character to be read as command input. A value of -1 means “empty.”
This variable is mostly obsolete now that you can use
unread-command-eventsinstead; it exists only to support programs written for Emacs versions 18 and earlier.
This function determines whether any command input is currently available to be read. It returns immediately, with value
tif there is available input,nilotherwise. On rare occasions it may returntwhen no input is available.
This variable records the last terminal input event read, whether as part of a command or explicitly by a Lisp program.
In the example below, the Lisp program reads the character 1, ASCII code 49. It becomes the value of
last-input-event, while C-e (we assume C-x C-e command is used to evaluate this expression) remains the value oflast-command-event.(progn (print (read-char)) (print last-command-event) last-input-event) -| 49 -| 5 ⇒ 49The alias
last-input-charis obsolete.
This construct runs the body forms and returns the value of the last one—but only if no input arrives. If any input arrives during the execution of the body forms, it aborts them (working much like a quit). The
while-no-inputform returnsnilif aborted by a real quit, and returnstif aborted by arrival of other input.If a part of body binds
inhibit-quitto non-nil, arrival of input during those parts won't cause an abort until the end of that part.If you want to be able to distinguish all possible values computed by body from both kinds of abort conditions, write the code like this:
(while-no-input (list (progn . body)))
This function discards the contents of the terminal input buffer and cancels any keyboard macro that might be in the process of definition. It returns
nil.In the following example, the user may type a number of characters right after starting the evaluation of the form. After the
sleep-forfinishes sleeping,discard-inputdiscards any characters typed during the sleep.(progn (sleep-for 2) (discard-input)) ⇒ nil
Special events are handled at a very low level—as soon as they are
read. The read-event function processes these events itself, and
never returns them. Instead, it keeps waiting for the first event
that is not special and returns that one.
Events that are handled in this way do not echo, they are never grouped
into key sequences, and they never appear in the value of
last-command-event or (this-command-keys). They do not
discard a numeric argument, they cannot be unread with
unread-command-events, they may not appear in a keyboard macro,
and they are not recorded in a keyboard macro while you are defining
one.
These events do, however, appear in last-input-event immediately
after they are read, and this is the way for the event's definition to
find the actual event.
The events types iconify-frame, make-frame-visible,
delete-frame, drag-n-drop, and user signals like
sigusr1 are normally handled in this way. The keymap which
defines how to handle special events—and which events are special—is
in the variable special-event-map (see Active Keymaps).
The wait functions are designed to wait for a certain amount of time
to pass or until there is input. For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
sit-for pauses and updates the screen, and returns immediately if
input comes in, while sleep-for pauses without updating the
screen.
This function performs redisplay (provided there is no pending input from the user), then waits seconds seconds, or until input is available. The usual purpose of
sit-foris to give the user time to read text that you display. The value istifsit-forwaited the full time with no input arriving (see Event Input Misc). Otherwise, the value isnil.The argument seconds need not be an integer. If it is a floating point number,
sit-forwaits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The expression
(sit-for 0)is equivalent to(redisplay), i.e. it requests a redisplay, without any delay, if there is no pending input. See Forcing Redisplay.If nodisp is non-
nil, thensit-fordoes not redisplay, but it still returns as soon as input is available (or when the timeout elapses).In batch mode (see Batch Mode),
sit-forcannot be interrupted, even by input from the standard input descriptor. It is thus equivalent tosleep-for, which is described below.It is also possible to call
sit-forwith three arguments, as(sit-forseconds millisec nodisp), but that is considered obsolete.
This function simply pauses for seconds seconds without updating the display. It pays no attention to available input. It returns
nil.The argument seconds need not be an integer. If it is a floating point number,
sleep-forwaits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
Use
sleep-forwhen you wish to guarantee a delay.
See Time of Day, for functions to get the current time.
Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop.
Typing C-g while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character. In the
simplest case, you cannot tell the difference, because C-g
normally runs the command keyboard-quit, whose effect is to quit.
However, when C-g follows a prefix key, they combine to form an
undefined key. The effect is to cancel the prefix key as well as any
prefix argument.
In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g always quit directly.
When C-g does directly quit, it does so by setting the variable
quit-flag to t. Emacs checks this variable at appropriate
times and quits if it is not nil. Setting quit-flag
non-nil in any way thus causes a quit.
At the level of C code, quitting cannot happen just anywhere; only at the
special places that check quit-flag. The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state. Because quitting is delayed until a safe place, quitting
cannot make Emacs crash.
Certain functions such as read-key-sequence or
read-quoted-char prevent quitting entirely even though they wait
for input. Instead of quitting, C-g serves as the requested
input. In the case of read-key-sequence, this serves to bring
about the special behavior of C-g in the command loop. In the
case of read-quoted-char, this is so that C-q can be used
to quote a C-g.
You can prevent quitting for a portion of a Lisp function by binding
the variable inhibit-quit to a non-nil value. Then,
although C-g still sets quit-flag to t as usual, the
usual result of this—a quit—is prevented. Eventually,
inhibit-quit will become nil again, such as when its
binding is unwound at the end of a let form. At that time, if
quit-flag is still non-nil, the requested quit happens
immediately. This behavior is ideal when you wish to make sure that
quitting does not happen within a “critical section” of the program.
In some functions (such as read-quoted-char), C-g is
handled in a special way that does not involve quitting. This is done
by reading the input with inhibit-quit bound to t, and
setting quit-flag to nil before inhibit-quit
becomes nil again. This excerpt from the definition of
read-quoted-char shows how this is done; it also shows that
normal quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)
"...documentation..."
(let ((message-log-max nil) done (first t) (code 0) char)
(while (not done)
(let ((inhibit-quit first)
...)
(and prompt (message "%s-" prompt))
(setq char (read-event))
(if inhibit-quit (setq quit-flag nil)))
...set the variable code...)
code))
If this variable is non-
nil, then Emacs quits immediately, unlessinhibit-quitis non-nil. Typing C-g ordinarily setsquit-flagnon-nil, regardless ofinhibit-quit.
This variable determines whether Emacs should quit when
quit-flagis set to a value other thannil. Ifinhibit-quitis non-nil, thenquit-flaghas no special effect.
This macro executes body forms in sequence, but allows quitting, at least locally, within body even if
inhibit-quitwas non-niloutside this construct. It returns the value of the last form in body, unless exited by quitting, in which case it returnsnil.If
inhibit-quitisnilon entry towith-local-quit, it only executes the body, and settingquit-flagcauses a normal quit. However, ifinhibit-quitis non-nilso that ordinary quitting is delayed, a non-nilquit-flagtriggers a special kind of local quit. This ends the execution of body and exits thewith-local-quitbody withquit-flagstill non-nil, so that another (ordinary) quit will happen as soon as that is allowed. Ifquit-flagis already non-nilat the beginning of body, the local quit happens immediately and the body doesn't execute at all.This macro is mainly useful in functions that can be called from timers, process filters, process sentinels,
pre-command-hook,post-command-hook, and other places whereinhibit-quitis normally bound tot.
This function signals the
quitcondition with(signal 'quit nil). This is the same thing that quitting does. (Seesignalin Errors.)
You can specify a character other than C-g to use for quitting.
See the function set-input-mode in Terminal Input.
Most Emacs commands can use a prefix argument, a number
specified before the command itself. (Don't confuse prefix arguments
with prefix keys.) The prefix argument is at all times represented by a
value, which may be nil, meaning there is currently no prefix
argument. Each command may use the prefix argument or ignore it.
There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation.
Here are the possible values of a raw prefix argument:
nil, meaning there is no prefix argument. Its numeric value is
1, but numerous commands make a distinction between nil and the
integer 1.
-. This indicates that M-- or C-u - was
typed, without following digits. The equivalent numeric value is
−1, but some commands make a distinction between the integer
−1 and the symbol -.
We illustrate these possibilities by calling the following function with various prefixes:
(defun display-prefix (arg)
"Display the value of the raw prefix arg."
(interactive "P")
(message "%s" arg))
Here are the results of calling display-prefix with various
raw prefix arguments:
M-x display-prefix -| nil
C-u M-x display-prefix -| (4)
C-u C-u M-x display-prefix -| (16)
C-u 3 M-x display-prefix -| 3
M-3 M-x display-prefix -| 3 ; (Same as C-u 3.)
C-u - M-x display-prefix -| -
M-- M-x display-prefix -| - ; (Same as C-u -.)
C-u - 7 M-x display-prefix -| -7
M-- 7 M-x display-prefix -| -7 ; (Same as C-u -7.)
Emacs uses two variables to store the prefix argument:
prefix-arg and current-prefix-arg. Commands such as
universal-argument that set up prefix arguments for other
commands store them in prefix-arg. In contrast,
current-prefix-arg conveys the prefix argument to the current
command, so setting it has no effect on the prefix arguments for future
commands.
Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the interactive specification.
(See Using Interactive.) Alternatively, functions may look at the
value of the prefix argument directly in the variable
current-prefix-arg, but this is less clean.
This function returns the numeric meaning of a valid raw prefix argument value, arg. The argument may be a symbol, a number, or a list. If it is
nil, the value 1 is returned; if it is-, the value −1 is returned; if it is a number, that number is returned; if it is a list, the car of that list (which should be a number) is returned.
This variable holds the raw prefix argument for the current command. Commands may examine it directly, but the usual method for accessing it is with
(interactive "P").
The value of this variable is the raw prefix argument for the next editing command. Commands such as
universal-argumentthat specify prefix arguments for the following command work by setting this variable.
The following commands exist to set up prefix arguments for the following command. Do not call them for any other reason.
This command reads input and specifies a prefix argument for the following command. Don't call this command yourself unless you know what you are doing.
This command adds to the prefix argument for the following command. The argument arg is the raw prefix argument as it was before this command; it is used to compute the updated prefix argument. Don't call this command yourself unless you know what you are doing.
This command adds to the numeric argument for the next command. The argument arg is the raw prefix argument as it was before this command; its value is negated to form the new prefix argument. Don't call this command yourself unless you know what you are doing.
The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command.
The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands.
To invoke a recursive editing level, call the function
recursive-edit. This function contains the command loop; it also
contains a call to catch with tag exit, which makes it
possible to exit the recursive editing level by throwing to exit
(see Catch and Throw). If you throw a value other than t,
then recursive-edit returns normally to the function that called
it. The command C-M-c (exit-recursive-edit) does this.
Throwing a t value causes recursive-edit to quit, so that
control returns to the command loop one level up. This is called
aborting, and is done by C-] (abort-recursive-edit).
Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to give the user different text to edit “recursively,” create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.)
Recursive edits are useful in debugging. You can insert a call to
debug into a function definition as a sort of breakpoint, so that
you can look around when the function gets there. debug invokes
a recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type C-r in
query-replace or use C-x q (kbd-macro-query).
This function invokes the editor command loop. It is called automatically by the initialization of Emacs, to let the user begin editing. When called from a Lisp program, it enters a recursive editing level.
If the current buffer is not the same as the selected window's buffer,
recursive-editsaves and restores the current buffer. Otherwise, if you switch buffers, the buffer you switched to is current afterrecursive-editreturns.In the following example, the function
simple-recfirst advances point one word, then enters a recursive edit, printing out a message in the echo area. The user can then do any editing desired, and then type C-M-c to exit and continue executingsimple-rec.(defun simple-rec () (forward-word 1) (message "Recursive edit in progress") (recursive-edit) (forward-word 1)) ⇒ simple-rec (simple-rec) ⇒ nil
This function exits from the innermost recursive edit (including minibuffer input). Its definition is effectively
(throw 'exit nil).
This function aborts the command that requested the innermost recursive edit (including minibuffer input), by signaling
quitafter exiting the recursive edit. Its definition is effectively(throw 'exit t). See Quitting.
This function exits all recursive editing levels; it does not return a value, as it jumps completely out of any computation directly back to the main command loop.
This function returns the current depth of recursive edits. When no recursive edit is active, it returns 0.
Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.
The low-level mechanism for disabling a command is to put a
non-nil disabled property on the Lisp symbol for the
command. These properties are normally set up by the user's
init file (see Init File) with Lisp expressions such as this:
(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default (you can remove them in your init file if you wish).
If the value of the disabled property is a string, the message
saying the command is disabled includes that string. For example:
(put 'delete-region 'disabled
"Text deleted this way cannot be yanked back!\n")
See Disabling, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs.
Allow command (a symbol) to be executed without special confirmation from now on, and alter the user's init file (see Init File) so that this will apply to future sessions.
Require special confirmation to execute command from now on, and alter the user's init file so that this will apply to future sessions.
The value of this variable should be a function. When the user invokes a disabled command interactively, this function is called instead of the disabled command. It can use
this-command-keysto determine what the user typed to run the command, and thus find the command itself.The value may also be
nil. Then all commands work normally, even disabled ones.By default, the value is a function that asks the user whether to proceed.
The command loop keeps a history of the complex commands that have
been executed, to make it convenient to repeat these commands. A
complex command is one for which the interactive argument reading
uses the minibuffer. This includes any M-x command, any
M-: command, and any command whose interactive
specification reads an argument from the minibuffer. Explicit use of
the minibuffer during the execution of the command itself does not cause
the command to be considered complex.
This variable's value is a list of recent complex commands, each represented as a form to evaluate. It continues to accumulate all complex commands for the duration of the editing session, but when it reaches the maximum size (see Minibuffer History), the oldest elements are deleted as new ones are added.
command-history ⇒ ((switch-to-buffer "chistory.texi") (describe-key "^X^[") (visit-tags-table "~/emacs/src/") (find-tag "repeat-complex-command"))
This history list is actually a special case of minibuffer history (see Minibuffer History), with one special twist: the elements are expressions rather than strings.
There are a number of commands devoted to the editing and recall of
previous commands. The commands repeat-complex-command, and
list-command-history are described in the user manual
(see Repetition). Within the
minibuffer, the usual minibuffer history commands are available.
A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don't confuse keyboard macros with Lisp macros (see Macros).
This function executes kbdmacro as a sequence of events. If kbdmacro is a string or vector, then the events in it are executed exactly as if they had been input by the user. The sequence is not expected to be a single key sequence; normally a keyboard macro definition consists of several key sequences concatenated.
If kbdmacro is a symbol, then its function definition is used in place of kbdmacro. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled.
The argument count is a repeat count; kbdmacro is executed that many times. If count is omitted or
nil, kbdmacro is executed once. If it is 0, kbdmacro is executed over and over until it encounters an error or a failing search.If loopfunc is non-
nil, it is a function that is called, without arguments, prior to each iteration of the macro. If loopfunc returnsnil, then this stops execution of the macro.See Reading One Event, for an example of using
execute-kbd-macro.
This variable contains the string or vector that defines the keyboard macro that is currently executing. It is
nilif no macro is currently executing. A command can test this variable so as to behave differently when run from an executing macro. Do not set this variable yourself.
This variable is non-
nilif and only if a keyboard macro is being defined. A command can test this variable so as to behave differently while a macro is being defined. The value isappendwhile appending to the definition of an existing macro. The commandsstart-kbd-macro,kmacro-start-macroandend-kbd-macroset this variable—do not set it yourself.The variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
This variable is the definition of the most recently defined keyboard macro. Its value is a string or vector, or
nil.The variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
This normal hook (see Standard Hooks) is run when a keyboard macro terminates, regardless of what caused it to terminate (reaching the macro end or an error which ended the macro prematurely).
The command bindings of input events are recorded in data structures called keymaps. Each entry in a keymap associates (or binds) an individual event type, either to another keymap or to a command. When an event type is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup.
A key sequence, or key for short, is a sequence of one or more input events that form a unit. Input events include characters, function keys, and mouse actions (see Input Events). The Emacs Lisp representation for a key sequence is a string or vector. Unless otherwise stated, any Emacs Lisp function that accepts a key sequence as an argument can handle both representations.
In the string representation, alphanumeric characters ordinarily
stand for themselves; for example, "a" represents a
and "2" represents 2. Control character events are
prefixed by the substring "\C-", and meta characters by
"\M-"; for example, "\C-x" represents the key C-x.
In addition, the <TAB>, <RET>, <ESC>, and <DEL> events
are represented by "\t", "\r", "\e", and
"\d" respectively. The string representation of a complete key
sequence is the concatenation of the string representations of the
constituent events; thus, "\C-xl" represents the key sequence
C-x l.
Key sequences containing function keys, mouse button events, or non-ASCII characters such as C-= or H-a cannot be represented as strings; they have to be represented as vectors.
In the vector representation, each element of the vector represents
an input event, in its Lisp form. See Input Events. For example,
the vector [?\C-x ?l] represents the key sequence C-x l.
For examples of key sequences written in string and vector representations, Init Rebinding.
This macro converts the text keyseq-text (a string constant) into a key sequence (a string or vector constant). The contents of keyseq-text should describe the key sequence using almost the same syntax used in this manual. More precisely, it uses the same syntax that Edit Macro mode uses for editing keyboard macros (see Edit Keyboard Macro); you must surround function key names with ‘<...>’.
(kbd "C-x") ⇒ "\C-x" (kbd "C-x C-f") ⇒ "\C-x\C-f" (kbd "C-x 4 C-f") ⇒ "\C-x4\C-f" (kbd "X") ⇒ "X" (kbd "RET") ⇒ "\^M" (kbd "C-c SPC") ⇒ "\C-c " (kbd "<f1> SPC") ⇒ [f1 32] (kbd "C-M-<down>") ⇒ [C-M-down]This macro is not meant for use with arguments that vary—only with string constants.
A keymap is a Lisp data structure that specifies key bindings for various key sequences.
A single keymap directly specifies definitions for individual events. When a key sequence consists of a single event, its binding in a keymap is the keymap's definition for that event. The binding of a longer key sequence is found by an iterative process: first find the definition of the first event (which must itself be a keymap); then find the second event's definition in that keymap, and so on until all the events in the key sequence have been processed.
If the binding of a key sequence is a keymap, we call the key sequence
a prefix key. Otherwise, we call it a complete key (because
no more events can be added to it). If the binding is nil,
we call the key undefined. Examples of prefix keys are C-c,
C-x, and C-x 4. Examples of defined complete keys are
X, <RET>, and C-x 4 C-f. Examples of undefined complete
keys are C-x C-g, and C-c 3. See Prefix Keys, for more
details.
The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit—it is not really one key sequence. In other words, removing one or more events from the end of any valid key sequence must always yield a prefix key. For example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key sequence.
The set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active—that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See Active Keymaps, for details.
Each keymap is a list whose car is the symbol keymap. The
remaining elements of the list define the key bindings of the keymap.
A symbol whose function definition is a keymap is also a keymap. Use
the function keymapp (see below) to test whether an object is a
keymap.
Several kinds of elements may appear in a keymap, after the symbol
keymap that begins it:
(type . binding)(type item-name [cache] . binding)(type item-name help-string [cache] . binding)(type menu-item . details)(t . binding)nil (see below).
When the binding is nil, it doesn't constitute a definition
but it does take precedence over a default binding or a binding in the
parent keymap. On the other hand, a binding of nil does
not override lower-precedence keymaps; thus, if the local map
gives a binding of nil, Emacs uses the binding from the
global map.
Keymaps do not directly record bindings for the meta characters.
Instead, meta characters are regarded for purposes of key lookup as
sequences of two characters, the first of which is <ESC> (or
whatever is currently the value of meta-prefix-char). Thus, the
key M-a is internally represented as <ESC> a, and its
global binding is found at the slot for a in esc-map
(see Prefix Keys).
This conversion applies only to characters, not to function keys or other input events; thus, M-<end> has nothing to do with <ESC> <end>.
Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for <DEL> and <TAB>, plus C-c C-l, M-C-q, and M-C-x.
lisp-mode-map
⇒
(keymap
(3 keymap
;; C-c C-z
(26 . run-lisp))
(27 keymap
;; M-C-x, treated as <ESC> C-x
(24 . lisp-send-defun)
keymap
;; M-C-q, treated as <ESC> C-q
(17 . indent-sexp))
;; This part is inherited from lisp-mode-shared-map.
keymap
;; <DEL>
(127 . backward-delete-char-untabify)
(27 keymap
;; M-C-q, treated as <ESC> C-q
(17 . indent-sexp))
(9 . lisp-indent-line))
This function returns
tif object is a keymap,nilotherwise. More precisely, this function tests for a list whose car iskeymap, or for a symbol whose function definition satisfieskeymapp.(keymapp '(keymap)) ⇒ t (fset 'foo '(keymap)) (keymapp 'foo) ⇒ t (keymapp (current-global-map)) ⇒ t
Here we describe the functions for creating keymaps.
This function creates and returns a new sparse keymap with no entries. (A sparse keymap is the kind of keymap you usually want.) The new keymap does not contain a char-table, unlike
make-keymap, and does not bind any events.(make-sparse-keymap) ⇒ (keymap)If you specify prompt, that becomes the overall prompt string for the keymap. You should specify this only for menu keymaps (see Defining Menus). A keymap with an overall prompt string will always present a mouse menu or a keyboard menu if it is active for looking up the next input event. Don't specify an overall prompt string for the main map of a major or minor mode, because that would cause the command loop to present a keyboard menu every time.
This function creates and returns a new full keymap. That keymap contains a char-table (see Char-Tables) with slots for all characters without modifiers. The new keymap initially binds all these characters to
nil, and does not bind any other kind of event. The argument prompt specifies a prompt string, as inmake-sparse-keymap.(make-keymap) ⇒ (keymap #^[t nil nil nil ... nil nil keymap])A full keymap is more efficient than a sparse keymap when it holds lots of bindings; for just a few, the sparse keymap is better.
This function returns a copy of keymap. Any keymaps that appear directly as bindings in keymap are also copied recursively, and so on to any number of levels. However, recursive copying does not take place when the definition of a character is a symbol whose function definition is a keymap; the same symbol appears in the new copy.
(setq map (copy-keymap (current-local-map))) ⇒ (keymap ;; (This implements meta characters.) (27 keymap (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) (eq map (current-local-map)) ⇒ nil (equal map (current-local-map)) ⇒ t
A keymap can inherit the bindings of another keymap, which we call the parent keymap. Such a keymap looks like this:
(keymap elements... . parent-keymap)
The effect is that this keymap inherits all the bindings of parent-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with elements.
If you change the bindings in parent-keymap using
define-key or other key-binding functions, these changed
bindings are visible in the inheriting keymap, unless shadowed by the
bindings made by elements. The converse is not true: if you use
define-key to change bindings in the inheriting keymap, these
changes are recorded in elements, but have no effect on
parent-keymap.
The proper way to construct a keymap with a parent is to use
set-keymap-parent; if you have code that directly constructs a
keymap with a parent, please convert the program to use
set-keymap-parent instead.
This returns the parent keymap of keymap. If keymap has no parent,
keymap-parentreturnsnil.
This sets the parent keymap of keymap to parent, and returns parent. If parent is
nil, this function gives keymap no parent at all.If keymap has submaps (bindings for prefix keys), they too receive new parent keymaps that reflect what parent specifies for those prefix keys.
Here is an example showing how to make a keymap that inherits
from text-mode-map:
(let ((map (make-sparse-keymap)))
(set-keymap-parent map text-mode-map)
map)
A non-sparse keymap can have a parent too, but this is not very
useful. A non-sparse keymap always specifies something as the binding
for every numeric character code without modifier bits, even if it is
nil, so these character's bindings are never inherited from
the parent keymap.
A prefix key is a key sequence whose binding is a keymap. The
keymap defines what to do with key sequences that extend the prefix key.
For example, C-x is a prefix key, and it uses a keymap that is
also stored in the variable ctl-x-map. This keymap defines
bindings for key sequences starting with C-x.
Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables:
esc-map is the global keymap for the <ESC> prefix key. Thus,
the global definitions of all meta characters are actually found here.
This map is also the function definition of ESC-prefix.
help-map is the global keymap for the C-h prefix key.
mode-specific-map is the global keymap for the prefix key
C-c. This map is actually global, not mode-specific, but its name
provides useful information about C-c in the output of C-h b
(display-bindings), since the main use of this prefix key is for
mode-specific bindings.
ctl-x-map is the global keymap used for the C-x prefix key.
This map is found via the function cell of the symbol
Control-X-prefix.
mule-keymap is the global keymap used for the C-x <RET>
prefix key.
ctl-x-4-map is the global keymap used for the C-x 4 prefix
key.
ctl-x-5-map is the global keymap used for the C-x 5 prefix
key.
2C-mode-map is the global keymap used for the C-x 6 prefix
key.
vc-prefix-map is the global keymap used for the C-x v prefix
key.
goto-map is the global keymap used for the M-g prefix
key.
search-map is the global keymap used for the M-s prefix
key.
facemenu-keymap is the global keymap used for the M-o
prefix key.
The keymap binding of a prefix key is used for looking up the event
that follows the prefix key. (It may instead be a symbol whose function
definition is a keymap. The effect is the same, but the symbol serves
as a name for the prefix key.) Thus, the binding of C-x is the
symbol Control-X-prefix, whose function cell holds the keymap
for C-x commands. (The same keymap is also the value of
ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and <ESC> as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See Active Keymaps.
If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then
the binding for C-p C-f is the function find-file, just
like C-x C-f. The key sequence C-p 6 is not found in any
active keymap.
(use-local-map (make-sparse-keymap))
⇒ nil
(local-set-key "\C-p" ctl-x-map)
⇒ nil
(key-binding "\C-p\C-f")
⇒ find-file
(key-binding "\C-p6")
⇒ nil
This function prepares symbol for use as a prefix key's binding: it creates a sparse keymap and stores it as symbol's function definition. Subsequently binding a key sequence to symbol will make that key sequence into a prefix key. The return value is
symbol.This function also sets symbol as a variable, with the keymap as its value. But if mapvar is non-
nil, it sets mapvar as a variable instead.If prompt is non-
nil, that becomes the overall prompt string for the keymap. The prompt string should be given for menu keymaps (see Defining Menus).
Emacs normally contains many keymaps; at any given time, just a few of them are active, meaning that they participate in the interpretation of user input. All the active keymaps are used together to determine what command to execute when a key is entered.
Normally the active keymaps are the keymap property keymap,
the keymaps of any enabled minor modes, the current buffer's local
keymap, and the global keymap, in that order. Emacs searches for each
input key sequence in all these keymaps. See Searching Keymaps,
for more details of this procedure.
When the key sequence starts with a mouse event (optionally preceded
by a symbolic prefix), the active keymaps are determined based on the
position in that event. If the event happened on a string embedded
with a display, before-string, or after-string
property (see Special Properties), the non-nil map
properties of the string override those of the buffer (if the
underlying buffer text contains map properties in its text properties
or overlays, they are ignored).
The global keymap holds the bindings of keys that are defined
regardless of the current buffer, such as C-f. The variable
global-map holds this keymap, which is always active.
Each buffer may have another keymap, its local keymap, which
may contain new or overriding definitions for keys. The current
buffer's local keymap is always active except when
overriding-local-map overrides it. The local-map text
or overlay property can specify an alternative local keymap for certain
parts of the buffer; see Special Properties.
Each minor mode can have a keymap; if it does, the keymap is active
when the minor mode is enabled. Modes for emulation can specify
additional active keymaps through the variable
emulation-mode-map-alists.
The highest precedence normal keymap comes from the keymap
text or overlay property. If that is non-nil, it is the first
keymap to be processed, in normal circumstances.
However, there are also special ways for programs to substitute
other keymaps for some of those. The variable
overriding-local-map, if non-nil, specifies a keymap
that replaces all the usual active keymaps except the global keymap.
Another way to do this is with overriding-terminal-local-map;
it operates on a per-terminal basis. These variables are documented
below.
Since every buffer that uses the same major mode normally uses the
same local keymap, you can think of the keymap as local to the mode. A
change to the local keymap of a buffer (using local-set-key, for
example) is seen also in the other buffers that share that keymap.
The local keymaps that are used for Lisp mode and some other major
modes exist even if they have not yet been used. These local keymaps are
the values of variables such as lisp-mode-map. For most major
modes, which are less frequently used, the local keymap is constructed
only when the mode is used for the first time in a session.
The minibuffer has local keymaps, too; they contain various completion and exit commands. See Intro to Minibuffers.
Emacs has other keymaps that are used in a different way—translating
events within read-key-sequence. See Translation Keymaps.
See Standard Keymaps, for a list of standard keymaps.
This returns the list of active keymaps that would be used by the command loop in the current circumstances to look up a key sequence. Normally it ignores
overriding-local-mapandoverriding-terminal-local-map, but if olp is non-nilthen it pays attention to them. position can optionally be either an event position as returned byevent-startor a buffer position, and may change the keymaps as described forkey-binding.
This function returns the binding for key according to the current active keymaps. The result is
nilif key is undefined in the keymaps.The argument accept-defaults controls checking for default bindings, as in
lookup-key(see Functions for Key Lookup).When commands are remapped (see Remapping Commands),
key-bindingnormally processes command remappings so as to returns the remapped command that will actually be executed. However, if no-remap is non-nil,key-bindingignores remappings and returns the binding directly specified for key.If key starts with a mouse event (perhaps following a prefix event), the maps to be consulted are determined based on the event's position. Otherwise, they are determined based on the value of point. However, you can override either of them by specifying position. If position is non-
nil, it should be either a buffer position or an event position like the value ofevent-start. Then the maps consulted are determined based on position.An error is signaled if key is not a string or a vector.
(key-binding "\C-x\C-f") ⇒ find-file
After translation of event subsequences (see Translation Keymaps) Emacs looks for them in the active keymaps. Here is a pseudo-Lisp description of the order and conditions for searching them:
(or (if overriding-terminal-local-map
(find-in overriding-terminal-local-map)
(if overriding-local-map
(find-in overriding-local-map)
(or (find-in (get-char-property (point) 'keymap))
(find-in-any emulation-mode-map-alists)
(find-in-any minor-mode-overriding-map-alist)
(find-in-any minor-mode-map-alist)
(if (get-text-property (point) 'local-map)
(find-in (get-char-property (point) 'local-map))
(find-in (current-local-map))))))
(find-in (current-global-map)))
The find-in and find-in-any are pseudo functions that
search in one keymap and in an alist of keymaps, respectively.
(Searching a single keymap for a binding is called key lookup;
see Key Lookup.) If the key sequence starts with a mouse event,
or a symbolic prefix event followed by a mouse event, that event's
position is used instead of point and the current buffer. Mouse
events on an embedded string use non-nil text properties from
that string instead of the buffer.
self-insert-command are translated
according to translation-table-for-input before insertion.
current-active-maps returns a list of the
currently active keymaps at point.
This variable contains the default global keymap that maps Emacs keyboard input to commands. The global keymap is normally this keymap. The default global keymap is a full keymap that binds
self-insert-commandto all of the printing characters.It is normal practice to change the bindings in the global keymap, but you should not assign this variable any value other than the keymap it starts out with.
This function returns the current global keymap. This is the same as the value of
global-mapunless you change one or the other. The return value is a reference, not a copy; if you usedefine-keyor other functions on it you will alter global bindings.(current-global-map) ⇒ (keymap [set-mark-command beginning-of-line ... delete-backward-char])
This function returns the current buffer's local keymap, or
nilif it has none. In the following example, the keymap for the ‘*scratch*’ buffer (using Lisp Interaction mode) is a sparse keymap in which the entry for <ESC>, ASCII code 27, is another sparse keymap.(current-local-map) ⇒ (keymap (10 . eval-print-last-sexp) (9 . lisp-indent-line) (127 . backward-delete-char-untabify) (27 keymap (24 . eval-defun) (17 . indent-sexp)))
current-local-map returns a reference to the local keymap, not
a copy of it; if you use define-key or other functions on it
you will alter local bindings.
This function returns a list of the keymaps of currently enabled minor modes.
This function makes keymap the new current global keymap. It returns
nil.It is very unusual to change the global keymap.
This function makes keymap the new local keymap of the current buffer. If keymap is
nil, then the buffer has no local keymap.use-local-mapreturnsnil. Most major mode commands use this function.
This variable is an alist describing keymaps that may or may not be active according to the values of certain variables. Its elements look like this:
(variable . keymap)The keymap keymap is active whenever variable has a non-
nilvalue. Typically variable is the variable that enables or disables a minor mode. See Keymaps and Minor Modes.Note that elements of
minor-mode-map-alistdo not have the same structure as elements ofminor-mode-alist. The map must be the cdr of the element; a list with the map as the second element will not do. The cdr can be either a keymap (a list) or a symbol whose function definition is a keymap.When more than one minor mode keymap is active, the earlier one in
minor-mode-map-alisttakes priority. But you should design minor modes so that they don't interfere with each other. If you do this properly, the order will not matter.See Keymaps and Minor Modes, for more information about minor modes. See also
minor-mode-key-binding(see Functions for Key Lookup).
This variable allows major modes to override the key bindings for particular minor modes. The elements of this alist look like the elements of
minor-mode-map-alist:(variable.keymap).If a variable appears as an element of
minor-mode-overriding-map-alist, the map specified by that element totally replaces any map specified for the same variable inminor-mode-map-alist.
minor-mode-overriding-map-alistis automatically buffer-local in all buffers.
If non-
nil, this variable holds a keymap to use instead of the buffer's local keymap, any text property or overlay keymaps, and any minor mode keymaps. This keymap, if specified, overrides all other maps that would have been active, except for the current global map.
If non-
nil, this variable holds a keymap to use instead ofoverriding-local-map, the buffer's local keymap, text property or overlay keymaps, and all the minor mode keymaps.This variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals. It is used to implement incremental search mode.
If this variable is non-
nil, the value ofoverriding-local-maporoverriding-terminal-local-mapcan affect the display of the menu bar. The default value isnil, so those map variables have no effect on the menu bar.Note that these two map variables do affect the execution of key sequences entered using the menu bar, even if they do not affect the menu bar display. So if a menu bar key sequence comes in, you should clear the variables before looking up and executing that key sequence. Modes that use the variables would typically do this anyway; normally they respond to events that they do not handle by “unreading” them and exiting.
This variable holds a keymap for special events. If an event type has a binding in this keymap, then it is special, and the binding for the event is run directly by
read-event. See Special Events.
This variable holds a list of keymap alists to use for emulations modes. It is intended for modes or packages using multiple minor-mode keymaps. Each element is a keymap alist which has the same format and meaning as
minor-mode-map-alist, or a symbol with a variable binding which is such an alist. The “active” keymaps in each alist are used beforeminor-mode-map-alistandminor-mode-overriding-map-alist.
Key lookup is the process of finding the binding of a key sequence from a given keymap. The execution or use of the binding is not part of key lookup.
Key lookup uses just the event type of each event in the key sequence;
the rest of the event is ignored. In fact, a key sequence used for key
lookup may designate a mouse event with just its types (a symbol)
instead of the entire event (a list). See Input Events. Such
a “key sequence” is insufficient for command-execute to run,
but it is sufficient for looking up or rebinding a key.
When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.
Let's use the term keymap entry to describe the value found by
looking up an event type in a keymap. (This doesn't include the item
string and other extra elements in a keymap element for a menu item, because
lookup-key and other key lookup functions don't include them in
the returned value.) While any Lisp object may be stored in a keymap
as a keymap entry, not all make sense for key lookup. Here is a table
of the meaningful types of keymap entries:
nilnil means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at all, and
has no default binding, that is equivalent to a binding of nil
for that event type.
keymap, then the list
is a keymap, and is treated as a keymap (see above).
lambda, then the list is a
lambda expression. This is presumed to be a function, and is treated
as such (see above). In order to execute properly as a key binding,
this function must be a command—it must have an interactive
specification. See Defining Commands.
(othermap . othertype)
When key lookup encounters an indirect entry, it looks up instead the binding of othertype in othermap and uses that.
This feature permits you to define one key as an alias for another key.
For example, an entry whose car is the keymap called esc-map
and whose cdr is 32 (the code for <SPC>) means, “Use the global
binding of Meta-<SPC>, whatever that may be.”
Note that keymaps and keyboard macros (strings and vectors) are not
valid functions, so a symbol with a keymap, string, or vector as its
function definition is invalid as a function. It is, however, valid as
a key binding. If the definition is a keyboard macro, then the symbol
is also valid as an argument to command-execute
(see Interactive Call).
The symbol undefined is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and its
binding is the command undefined; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling ding) but does not signal an error.
undefined is used in local keymaps to override a global key
binding and make the key “undefined” locally. A local binding of
nil would fail to do this because it would not override the
global binding.
In short, a keymap entry may be a keymap, a command, a keyboard macro,
a symbol that leads to one of them, or an indirection or nil.
Here is an example of a sparse keymap with two characters bound to
commands and one bound to another keymap. This map is the normal value
of emacs-lisp-mode-map. Note that 9 is the code for <TAB>,
127 for <DEL>, 27 for <ESC>, 17 for C-q and 24 for
C-x.
(keymap (9 . lisp-indent-line)
(127 . backward-delete-char-untabify)
(27 keymap (17 . indent-sexp) (24 . eval-defun)))
Here are the functions and variables pertaining to key lookup.
This function returns the definition of key in keymap. All the other functions described in this chapter that look up keys use
lookup-key. Here are examples:(lookup-key (current-global-map) "\C-x\C-f") ⇒ find-file (lookup-key (current-global-map) (kbd "C-x C-f")) ⇒ find-file (lookup-key (current-global-map) "\C-x\C-f12345") ⇒ 2If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap, it must be “too long” and have extra events at the end that do not fit into a single key sequence. Then the value is a number, the number of events at the front of key that compose a complete key.
If accept-defaults is non-
nil, thenlookup-keyconsiders default bindings as well as bindings for the specific events in key. Otherwise,lookup-keyreports only bindings for the specific sequence key, ignoring default bindings except when you explicitly ask about them. (To do this, supplytas an element of key; see Format of Keymaps.)If key contains a meta character (not a function key), that character is implicitly replaced by a two-character sequence: the value of
meta-prefix-char, followed by the corresponding non-meta character. Thus, the first example below is handled by conversion into the second example.(lookup-key (current-global-map) "\M-f") ⇒ forward-word (lookup-key (current-global-map) "\ef") ⇒ forward-wordUnlike
read-key-sequence, this function does not modify the specified events in ways that discard information (see Key Sequence Input). In particular, it does not convert letters to lower case and it does not change drag events to clicks.
This function returns the binding for key in the current local keymap, or
nilif it is undefined there.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This function returns the binding for command key in the current global keymap, or
nilif it is undefined there.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This function returns a list of all the active minor mode bindings of key. More precisely, it returns an alist of pairs
(modename.binding), where modename is the variable that enables the minor mode, and binding is key's binding in that mode. If key has no minor-mode bindings, the value isnil.If the first binding found is not a prefix definition (a keymap or a symbol defined as a keymap), all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.
The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This variable is the meta-prefix character code. It is used for translating a meta character to a two-character sequence so it can be looked up in a keymap. For useful results, the value should be a prefix event (see Prefix Keys). The default value is 27, which is the ASCII code for <ESC>.
As long as the value of
meta-prefix-charremains 27, key lookup translates M-b into <ESC> b, which is normally defined as thebackward-wordcommand. However, if you were to setmeta-prefix-charto 24, the code for C-x, then Emacs will translate M-b into C-x b, whose standard binding is theswitch-to-buffercommand. (Don't actually do this!) Here is an illustration of what would happen:meta-prefix-char ; The default value. ⇒ 27 (key-binding "\M-b") ⇒ backward-word ?\C-x ; The print representation ⇒ 24 ; of a character. (setq meta-prefix-char 24) ⇒ 24 (key-binding "\M-b") ⇒ switch-to-buffer ; Now, typing M-b is ; like typing C-x b. (setq meta-prefix-char 27) ; Avoid confusion! ⇒ 27 ; Restore the default value!This translation of one event into two happens only for characters, not for other kinds of input events. Thus, M-<F1>, a function key, is not converted into <ESC> <F1>.
The way to rebind a key is to change its entry in a keymap. If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one). If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The global-set-key and local-set-key functions are
convenient interfaces for these operations (see Key Binding Commands). You can also use define-key, a more general
function; then you must specify explicitly the map to change.
When choosing the key sequences for Lisp programs to rebind, please follow the Emacs conventions for use of various keys (see Key Binding Conventions).
In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (see 字符串类型).
The syntax ‘\C-’ means that the following character is a control
character and ‘\M-’ means that the following character is a meta
character. Thus, the string "\M-x" is read as containing a
single M-x, "\C-f" is read as containing a single
C-f, and "\M-\C-x" and "\C-\M-x" are both read as
containing a single C-M-x. You can also use this escape syntax in
vectors, as well as others that aren't allowed in strings; one example
is ‘[?\C-\H-x home]’. See 字符类型.
The key definition and lookup functions accept an alternate syntax for
event types in a key sequence that is a vector: you can use a list
containing modifier names plus one base event (a character or function
key name). For example, (control ?a) is equivalent to
?\C-a and (hyper control left) is equivalent to
C-H-left. One advantage of such lists is that the precise
numeric codes for the modifier bits don't appear in compiled files.
The functions below signal an error if keymap is not a keymap,
or if key is not a string or vector representing a key sequence.
You can use event types (symbols) as shorthand for events that are
lists. The kbd macro (see Key Sequences) is a convenient
way to specify the key sequence.
This function sets the binding for key in keymap. (If key is more than one event long, the change is actually made in another keymap reached from keymap.) The argument binding can be any Lisp object, but only certain types are meaningful. (For a list of meaningful types, see Key Lookup.) The value returned by
define-keyis binding.If key is
[t], this sets the default binding in keymap. When an event has no binding of its own, the Emacs command loop uses the keymap's default binding, if there is one.Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled. If some prefix of key is undefined, then
define-keydefines it as a prefix key so that the rest of key can be defined as specified.If there was previously no binding for key in keymap, the new binding is added at the beginning of keymap. The order of bindings in a keymap makes no difference for keyboard input, but it does matter for menu keymaps (see Menu Keymaps).
This example creates a sparse keymap and makes a number of bindings in it:
(setq map (make-sparse-keymap))
⇒ (keymap)
(define-key map "\C-f" 'forward-char)
⇒ forward-char
map
⇒ (keymap (6 . forward-char))
;; Build sparse submap for C-x and bind f in that.
(define-key map (kbd "C-x f") 'forward-word)
⇒ forward-word
map
⇒ (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map (kbd "C-p") ctl-x-map)
;; ctl-x-map
⇒ [nil ... find-file ... backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map (kbd "C-p C-f") 'foo)
⇒ 'foo
map
⇒ (keymap ; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for C-p C-f actually works by
changing an entry in ctl-x-map, and this has the effect of
changing the bindings of both C-p C-f and C-x C-f in the
default global map.
The function substitute-key-definition scans a keymap for
keys that have a certain binding and rebinds them with a different
binding. Another feature which is cleaner and can often produce the
same results to remap one command into another (see Remapping Commands).
This function replaces olddef with newdef for any keys in keymap that were bound to olddef. In other words, olddef is replaced with newdef wherever it appears. The function returns
nil.For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:
(substitute-key-definition 'find-file 'find-file-read-only (current-global-map))If oldmap is non-
nil, that changes the behavior ofsubstitute-key-definition: the bindings in oldmap determine which keys to rebind. The rebindings still happen in keymap, not in oldmap. Thus, you can change one map under the control of the bindings in another. For example,(substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map)puts the special deletion command in
my-mapfor whichever keys are globally bound to the standard deletion command.Here is an example showing a keymap before and after substitution:
(setq map '(keymap (?1 . olddef-1) (?2 . olddef-2) (?3 . olddef-1))) ⇒ (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1)) (substitute-key-definition 'olddef-1 'newdef map) ⇒ nil map ⇒ (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
This function changes the contents of the full keymap keymap by remapping
self-insert-commandto the commandundefined(see Remapping Commands). This has the effect of undefining all printing characters, thus making ordinary insertion of text impossible.suppress-keymapreturnsnil.If nodigits is
nil, thensuppress-keymapdefines digits to rundigit-argument, and - to runnegative-argument. Otherwise it makes them undefined like the rest of the printing characters.The
suppress-keymapfunction does not make it impossible to modify a buffer, as it does not suppress commands such asyankandquoted-insert. To prevent any modification of a buffer, make it read-only (see Read Only Buffers).Since this function modifies keymap, you would normally use it on a newly created keymap. Operating on an existing keymap that is used for some other purpose is likely to cause trouble; for example, suppressing
global-mapwould make it impossible to use most of Emacs.Most often,
suppress-keymapis used to initialize local keymaps of modes such as Rmail and Dired where insertion of text is not desirable and the buffer is read-only. Here is an example taken from the file emacs/lisp/dired.el, showing how the local keymap for Dired mode is set up:(setq dired-mode-map (make-keymap)) (suppress-keymap dired-mode-map) (define-key dired-mode-map "r" 'dired-rename-file) (define-key dired-mode-map "\C-d" 'dired-flag-file-deleted) (define-key dired-mode-map "d" 'dired-flag-file-deleted) (define-key dired-mode-map "v" 'dired-view-file) (define-key dired-mode-map "e" 'dired-find-file) (define-key dired-mode-map "f" 'dired-find-file) ...
A special kind of key binding, using a special “key sequence”
which includes a command name, has the effect of remapping that
command into another. Here's how it works. You make a key binding
for a key sequence that starts with the dummy event remap,
followed by the command name you want to remap. Specify the remapped
definition as the definition in this binding. The remapped definition
is usually a command name, but it can be any valid definition for
a key binding.
Here's an example. Suppose that My mode uses special commands
my-kill-line and my-kill-word, which should be invoked
instead of kill-line and kill-word. It can establish
this by making these two command-remapping bindings in its keymap:
(define-key my-mode-map [remap kill-line] 'my-kill-line)
(define-key my-mode-map [remap kill-word] 'my-kill-word)
Whenever my-mode-map is an active keymap, if the user types
C-k, Emacs will find the standard global binding of
kill-line (assuming nobody has changed it). But
my-mode-map remaps kill-line to my-kill-line,
so instead of running kill-line, Emacs runs
my-kill-line.
Remapping only works through a single level. In other words,
(define-key my-mode-map [remap kill-line] 'my-kill-line)
(define-key my-mode-map [remap my-kill-line] 'my-other-kill-line)
does not have the effect of remapping kill-line into
my-other-kill-line. If an ordinary key binding specifies
kill-line, this keymap will remap it to my-kill-line;
if an ordinary binding specifies my-kill-line, this keymap will
remap it to my-other-kill-line.
To undo the remapping of a command, remap it to nil; e.g.
(define-key my-mode-map [remap kill-line] nil)
This function returns the remapping for command (a symbol), given the current active keymaps. If command is not remapped (which is the usual situation), or not a symbol, the function returns
nil.positioncan optionally specify a buffer position or an event position to determine the keymaps to use, as inkey-binding.If the optional argument
keymapsis non-nil, it specifies a list of keymaps to search in. This argument is ignored ifpositionis non-nil.
This section describes keymaps that are used during reading a key
sequence, to translate certain event sequences into others.
read-key-sequence checks every subsequence of the key sequence
being read, as it is read, against input-decode-map, then
local-function-key-map, and then against key-translation-map.
This variable holds a keymap that describes the character sequences sent by function keys on an ordinary character terminal. This keymap has the same structure as other keymaps, but is used differently: it specifies translations to make while reading key sequences, rather than bindings for key sequences.
If
input-decode-map“binds” a key sequence k to a vector v, then when k appears as a subsequence anywhere in a key sequence, it is replaced with the events in v.For example, VT100 terminals send <ESC> O P when the keypad <PF1> key is pressed. Therefore, we want Emacs to translate that sequence of events into the single event
pf1. We accomplish this by “binding” <ESC> O P to[pf1]ininput-decode-map, when using a VT100.Thus, typing C-c <PF1> sends the character sequence C-c <ESC> O P; later the function
read-key-sequencetranslates this back into C-c <PF1>, which it returns as the vector[?\C-c pf1].The value of
input-decode-mapis usually set up automatically according to the terminal's Terminfo or Termcap entry, but sometimes those need help from terminal-specific Lisp files. Emacs comes with terminal-specific files for many common terminals; their main purpose is to make entries ininput-decode-mapbeyond those that can be deduced from Termcap and Terminfo. See Terminal-Specific.
This variable holds a keymap similar to
input-decode-mapexcept that it describes key sequences which should be translated to alternative interpretations that are usually preferred. It applies afterinput-decode-mapand beforekey-translation-map.Entries in
local-function-key-mapare ignored if they conflict with bindings made in the minor mode, local, or global keymaps. I.e. the remapping only applies if the original key sequence would otherwise not have any binding.
local-function-key-mapinherits fromfunction-key-map, but the latter should not be used directly.
This variable is another keymap used just like
input-decode-mapto translate input events into other events. It differs frominput-decode-mapin that it goes to work afterlocal-function-key-mapis finished rather than before; it receives the results of translation bylocal-function-key-map.Just like
input-decode-map, but unlikelocal-function-key-map, this keymap is applied regardless of whether the input key-sequence has a normal binding. Note however that actual key bindings can have an effect onkey-translation-map, even though they are overridden by it. Indeed, actual key bindings overridelocal-function-key-mapand thus may alter the key sequence thatkey-translation-mapreceives. Clearly, it is better to avoid this type of situation.The intent of
key-translation-mapis for users to map one character set to another, including ordinary characters normally bound toself-insert-command.
You can use input-decode-map, local-function-key-map, or
key-translation-map for more than simple aliases, by using a
function, instead of a key sequence, as the “translation” of a key.
Then this function is called to compute the translation of that key.
The key translation function receives one argument, which is the prompt
that was specified in read-key-sequence—or nil if the
key sequence is being read by the editor command loop. In most cases
you can ignore the prompt value.
If the function reads input itself, it can have the effect of altering the event that follows. For example, here's how to define C-c h to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key local-function-key-map "\C-ch" 'hyperify)
If you have enabled keyboard character set decoding using
set-keyboard-coding-system, decoding is done after the
translations listed above. See Terminal I/O Encoding. However, in
future Emacs versions, character set decoding may be done at an
earlier stage.
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling define-key.
People often use global-set-key in their init files
(see Init File) for simple customization. For example,
(global-set-key (kbd "C-x C-\\") 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
or
(global-set-key [(control ?x) (control ?\\)] 'next-line)
redefines C-x C-\ to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, entered with the Meta key, to set point where you click.
Be careful when using non-ASCII text characters in Lisp specifications of keys to bind. If these are read as multibyte text, as they usually will be in a Lisp file (see Loading Non-ASCII), you must type the keys as multibyte too. For instance, if you use this:
(global-set-key "ö" 'my-function) ; bind o-umlaut
or
(global-set-key ?ö 'my-function) ; bind o-umlaut
and your language environment is multibyte Latin-1, these commands actually bind the multibyte character with code 2294, not the unibyte Latin-1 character with code 246 (M-v). In order to use this binding, you need to enter the multibyte Latin-1 character as keyboard input. One way to do this is by using an appropriate input method (see Input Methods).
If you want to use a unibyte character in the key binding, you can
construct the key sequence string using multibyte-char-to-unibyte
or string-make-unibyte (see Converting Representations).
This function sets the binding of key in the current global map to binding.
(global-set-key key binding) == (define-key (current-global-map) key binding)
This function removes the binding of key from the current global map.
One use of this function is in preparation for defining a longer key that uses key as a prefix—which would not be allowed if key has a non-prefix binding. For example:
(global-unset-key "\C-l") ⇒ nil (global-set-key "\C-l\C-l" 'redraw-display) ⇒ nilThis function is implemented simply using
define-key:(global-unset-key key) == (define-key (current-global-map) key nil)
This function sets the binding of key in the current local keymap to binding.
(local-set-key key binding) == (define-key (current-local-map) key binding)
This function removes the binding of key from the current local map.
(local-unset-key key) == (define-key (current-local-map) key nil)
This section describes functions used to scan all the current keymaps for the sake of printing help information.
This function returns a list of all the keymaps that can be reached (via zero or more prefix keys) from keymap. The value is an association list with elements of the form
(key.map), where key is a prefix key whose definition in keymap is map.The elements of the alist are ordered so that the key increases in length. The first element is always
([] .keymap), because the specified keymap is accessible from itself with a prefix of no events.If prefix is given, it should be a prefix key sequence; then
accessible-keymapsincludes only the submaps whose prefixes start with prefix. These elements look just as they do in the value of(accessible-keymaps); the only difference is that some elements are omitted.In the example below, the returned alist indicates that the key <ESC>, which is displayed as ‘^[’, is a prefix key whose definition is the sparse keymap
(keymap (83 . center-paragraph) (115 . foo)).(accessible-keymaps (current-local-map)) ⇒(([] keymap (27 keymap ; Note this keymap for <ESC> is repeated below. (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) ("^[" keymap (83 . center-paragraph) (115 . foo)))In the following example, C-h is a prefix key that uses a sparse keymap starting with
(keymap (118 . describe-variable)...). Another prefix, C-x 4, uses a keymap which is also the value of the variablectl-x-4-map. The eventmode-lineis one of several dummy events used as prefixes for mouse actions in special parts of a window.(accessible-keymaps (current-global-map)) ⇒ (([] keymap [set-mark-command beginning-of-line ... delete-backward-char]) ("^H" keymap (118 . describe-variable) ... (8 . help-for-help)) ("^X" keymap [x-flush-mouse-queue ... backward-kill-sentence]) ("^[" keymap [mark-sexp backward-sexp ... backward-kill-word]) ("^X4" keymap (15 . display-buffer) ...) ([mode-line] keymap (S-mouse-2 . mouse-split-window-horizontally) ...))These are not all the keymaps you would see in actuality.
The function
map-keymapcalls function once for each binding in keymap. It passes two arguments, the event type and the value of the binding. If keymap has a parent, the parent's bindings are included as well. This works recursively: if the parent has itself a parent, then the grandparent's bindings are also included and so on.This function is the cleanest way to examine all the bindings in a keymap.
This function is a subroutine used by the
where-iscommand (see Help). It returns a list of all key sequences (of any length) that are bound to command in a set of keymaps.The argument command can be any object; it is compared with all keymap entries using
eq.If keymap is
nil, then the maps used are the current active keymaps, disregardingoverriding-local-map(that is, pretending its value isnil). If keymap is a keymap, then the maps searched are keymap and the global keymap. If keymap is a list of keymaps, only those keymaps are searched.Usually it's best to use
overriding-local-mapas the expression for keymap. Thenwhere-is-internalsearches precisely the keymaps that are active. To search only the global map, pass(keymap)(an empty keymap) as keymap.If firstonly is
non-ascii, then the value is a single vector representing the first key sequence found, rather than a list of all possible key sequences. If firstonly ist, then the value is the first key sequence, except that key sequences consisting entirely of ASCII characters (or meta variants of ASCII characters) are preferred to all other key sequences and that the return value can never be a menu binding.If noindirect is non-
nil,where-is-internaldoesn't follow indirect keymap bindings. This makes it possible to search for an indirect definition itself.When command remapping is in effect (see Remapping Commands),
where-is-internalfigures out when a command will be run due to remapping and reports keys accordingly. It also returnsnilif command won't really be run because it has been remapped to some other command. However, if no-remap is non-nil.where-is-internalignores remappings.(where-is-internal 'describe-function) ⇒ ([8 102] [f1 102] [help 102] [menu-bar help-menu describe describe-function])
This function creates a listing of all current key bindings, and displays it in a buffer named ‘*Help*’. The text is grouped by modes—minor modes first, then the major mode, then global bindings.
If prefix is non-
nil, it should be a prefix key; then the listing includes only keys that start with prefix.The listing describes meta characters as <ESC> followed by the corresponding non-meta character.
When several characters with consecutive ASCII codes have the same definition, they are shown together, as ‘firstchar..lastchar’. In this instance, you need to know the ASCII codes to understand which characters this means. For example, in the default global map, the characters ‘<SPC> .. ~’ are described by a single line. <SPC> is ASCII 32, ~ is ASCII 126, and the characters between them include all the normal printing characters, (e.g., letters, digits, punctuation, etc.); all these characters are bound to
self-insert-command.If buffer-or-name is non-
nil, it should be a buffer or a buffer name. Thendescribe-bindingslists that buffer's bindings, instead of the current buffer's.
A keymap can operate as a menu as well as defining bindings for keyboard keys and mouse buttons. Menus are usually actuated with the mouse, but they can function with the keyboard also. If a menu keymap is active for the next input event, that activates the keyboard menu feature.
A keymap acts as a menu if it has an overall prompt string, which is a string that appears as an element of the keymap. (See Format of Keymaps.) The string should describe the purpose of the menu's commands. Emacs displays the overall prompt string as the menu title in some cases, depending on the toolkit (if any) used for displaying menus.10 Keyboard menus also display the overall prompt string.
The easiest way to construct a keymap with a prompt string is to
specify the string as an argument when you call make-keymap,
make-sparse-keymap (see Creating Keymaps), or
define-prefix-command (see Definition of define-prefix-command). If you do not want the keymap to operate as
a menu, don't specify a prompt string for it.
This function returns the overall prompt string of keymap, or
nilif it has none.
The menu's items are the bindings in the keymap. Each binding associates an event type to a definition, but the event types have no significance for the menu appearance. (Usually we use pseudo-events, symbols that the keyboard cannot generate, as the event types for menu item bindings.) The menu is generated entirely from the bindings that correspond in the keymap to these events.
The order of items in the menu is the same as the order of bindings in
the keymap. Since define-key puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order. When you add an item to
an existing menu, you can specify its position in the menu using
define-key-after (see Modifying Menus).
The simpler (and original) way to define a menu item is to bind some event type (it doesn't matter what event type) to a binding like this:
(item-string . real-binding)
The car, item-string, is the string to be displayed in the menu. It should be short—preferably one to three words. It should describe the action of the command it corresponds to. Note that it is not generally possible to display non-ASCII text in menus. It will work for keyboard menus and will work to a large extent when Emacs is built with the Gtk+ toolkit.11
You can also supply a second string, called the help string, as follows:
(item-string help . real-binding)
help specifies a “help-echo” string to display while the mouse
is on that item in the same way as help-echo text properties
(see Help display).
As far as define-key is concerned, item-string and
help-string are part of the event's binding. However,
lookup-key returns just real-binding, and only
real-binding is used for executing the key.
If real-binding is nil, then item-string appears in
the menu but cannot be selected.
If real-binding is a symbol and has a non-nil
menu-enable property, that property is an expression that
controls whether the menu item is enabled. Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-nil. When a
menu item is disabled, it is displayed in a “fuzzy” fashion, and
cannot be selected.
The menu bar does not recalculate which items are enabled every time you
look at a menu. This is because the X toolkit requires the whole tree
of menus in advance. To force recalculation of the menu bar, call
force-mode-line-update (see Mode Line Format).
You've probably noticed that menu items show the equivalent keyboard key sequence (if any) to invoke the same command. To save time on recalculation, menu display caches this information in a sublist in the binding, like this:
(item-string [help] (key-binding-data) . real-binding)
Don't put these sublists in the menu item yourself; menu display calculates them automatically. Don't mention keyboard equivalents in the item strings themselves, since that is redundant.
An extended-format menu item is a more flexible and also cleaner
alternative to the simple format. You define an event type with a
binding that's a list starting with the symbol menu-item.
For a non-selectable string, the binding looks like this:
(menu-item item-name)
A string starting with two or more dashes specifies a separator line; see Menu Separators.
To define a real menu item which can be selected, the extended format binding looks like this:
(menu-item item-name real-binding
. item-property-list)
Here, item-name is an expression which evaluates to the menu item string. Thus, the string need not be a constant. The third element, real-binding, is the command to execute. The tail of the list, item-property-list, has the form of a property list which contains other information.
When an equivalent keyboard key binding is cached, the extended menu item binding looks like this:
(menu-item item-name real-binding (key-binding-data)
. item-property-list)
Here is a table of the properties that are supported:
:enable formnil means yes). If the item is not enabled,
you can't really click on it.
:visible formnil means yes). If the item
does not appear, then the menu is displayed as if this item were
not defined at all.
:help helphelp-echo text properties (see Help display).
Note that this must be a constant string, unlike the help-echo
property for text and overlays.
:button (type . selected):toggle or
:radio. The cdr, selected, should be a form; the
result of evaluating it says whether this button is currently selected.
A toggle is a menu item which is labeled as either “on” or “off”
according to the value of selected. The command itself should
toggle selected, setting it to t if it is nil,
and to nil if it is t. Here is how the menu item
to toggle the debug-on-error flag is defined:
(menu-item "Debug on Error" toggle-debug-on-error
:button (:toggle
. (and (boundp 'debug-on-error)
debug-on-error)))
This works because toggle-debug-on-error is defined as a command
which toggles the variable debug-on-error.
Radio buttons are a group of menu items, in which at any time one
and only one is “selected.” There should be a variable whose value
says which one is selected at any time. The selected form for
each radio button in the group should check whether the variable has the
right value for selecting that button. Clicking on the button should
set the variable so that the button you clicked on becomes selected.
:key-sequence key-sequenceIf you specify the wrong key sequence, it has no effect; before Emacs
displays key-sequence in the menu, it verifies that
key-sequence is really equivalent to this menu item.
:key-sequence nilHowever, if the user has rebound this item's definition to a key
sequence, Emacs ignores the :keys property and finds the keyboard
equivalent anyway.
:keys string:filter filter-fnEmacs can call this function at any time that it does redisplay or operates on menu data structures, so you should write it so it can safely be called at any time.
A menu separator is a kind of menu item that doesn't display any text—instead, it divides the menu into subparts with a horizontal line. A separator looks like this in the menu keymap:
(menu-item separator-type)
where separator-type is a string starting with two or more dashes.
In the simplest case, separator-type consists of only dashes.
That specifies the default kind of separator. (For compatibility,
"" and - also count as separators.)
Certain other values of separator-type specify a different style of separator. Here is a table of them:
"--no-line""--space""--single-line""--double-line""--single-dashed-line""--double-dashed-line""--shadow-etched-in""--shadow-etched-out""--shadow-etched-in-dash""--shadow-etched-out-dash""--shadow-double-etched-in""--shadow-double-etched-out""--shadow-double-etched-in-dash""--shadow-double-etched-out-dash"You can also give these names in another style, adding a colon after
the double-dash and replacing each single dash with capitalization of
the following word. Thus, "--:singleLine", is equivalent to
"--single-line".
Some systems and display toolkits don't really handle all of these separator types. If you use a type that isn't supported, the menu displays a similar kind of separator that is supported.
Sometimes it is useful to make menu items that use the “same”
command but with different enable conditions. The best way to do this
in Emacs now is with extended menu items; before that feature existed,
it could be done by defining alias commands and using them in menu
items. Here's an example that makes two aliases for
toggle-read-only and gives them different enable conditions:
(defalias 'make-read-only 'toggle-read-only)
(put 'make-read-only 'menu-enable '(not buffer-read-only))
(defalias 'make-writable 'toggle-read-only)
(put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the
equivalent key bindings for the “real” command name, not the aliases
(which typically don't have any key bindings except for the menu
itself). To request this, give the alias symbol a non-nil
menu-alias property. Thus,
(put 'make-read-only 'menu-alias t)
(put 'make-writable 'menu-alias t)
causes menu items for make-read-only and make-writable to
show the keyboard bindings for toggle-read-only.
The usual way to make a menu keymap produce a menu is to make it the definition of a prefix key. (A Lisp program can explicitly pop up a menu and receive the user's choice—see Pop-Up Menus.)
If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)
It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.
A single keymap can appear as multiple menu panes, if you explicitly arrange for this. The way to do this is to make a keymap for each pane, then create a binding for each of those maps in the main keymap of the menu. Give each of these bindings an item string that starts with ‘@’. The rest of the item string becomes the name of the pane. See the file lisp/mouse.el for an example of this. Any ordinary bindings with ‘@’-less item strings are grouped into one pane, which appears along with the other panes explicitly created for the submaps.
X toolkit menus don't have panes; instead, they can have submenus. Every nested keymap becomes a submenu, whether the item string starts with ‘@’ or not. In a toolkit version of Emacs, the only thing special about ‘@’ at the beginning of an item string is that the ‘@’ doesn't appear in the menu item.
Multiple keymaps that define the same menu prefix key produce separate panes or separate submenus.
When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the keymap operates as a keyboard menu; the user specifies the next event by choosing a menu item with the keyboard.
Emacs displays the keyboard menu with the map's overall prompt
string, followed by the alternatives (the item strings of the map's
bindings), in the echo area. If the bindings don't all fit at once,
the user can type <SPC> to see the next line of alternatives.
Successive uses of <SPC> eventually get to the end of the menu and
then cycle around to the beginning. (The variable
menu-prompt-more-char specifies which character is used for
this; <SPC> is the default.)
When the user has found the desired alternative from the menu, he or she should type the corresponding character—the one whose binding is that alternative.
This way of using menus in an Emacs-like editor was inspired by the Hierarkey system.
This variable specifies the character to use to ask to see the next line of a menu. Its initial value is 32, the code for <SPC>.
Here is a complete example of defining a menu keymap. It is the definition of the ‘Replace’ submenu in the ‘Edit’ menu in the menu bar, and it uses the extended menu item format (see Extended Menu Items). First we create the keymap, and give it a name:
(defvar menu-bar-replace-menu (make-sparse-keymap "Replace"))
Next we define the menu items:
(define-key menu-bar-replace-menu [tags-repl-continue]
'(menu-item "Continue Replace" tags-loop-continue
:help "Continue last tags replace operation"))
(define-key menu-bar-replace-menu [tags-repl]
'(menu-item "Replace in tagged files" tags-query-replace
:help "Interactively replace a regexp in all tagged files"))
(define-key menu-bar-replace-menu [separator-replace-tags]
'(menu-item "--"))
;; ...
Note the symbols which the bindings are “made for”; these appear
inside square brackets, in the key sequence being defined. In some
cases, this symbol is the same as the command name; sometimes it is
different. These symbols are treated as “function keys,” but they are
not real function keys on the keyboard. They do not affect the
functioning of the menu itself, but they are “echoed” in the echo area
when the user selects from the menu, and they appear in the output of
where-is and apropos.
The menu in this example is intended for use with the mouse. If a menu is intended for use with the keyboard, that is, if it is bound to a key sequence ending with a keyboard event, then the menu items should be bound to characters or “real” function keys, that can be typed with the keyboard.
The binding whose definition is ("--") is a separator line.
Like a real menu item, the separator has a key symbol, in this case
separator-replace-tags. If one menu has two separators, they
must have two different key symbols.
Here is how we make this menu appear as an item in the parent menu:
(define-key menu-bar-edit-menu [replace]
(list 'menu-item "Replace" menu-bar-replace-menu))
Note that this incorporates the submenu keymap, which is the value of
the variable menu-bar-replace-menu, rather than the symbol
menu-bar-replace-menu itself. Using that symbol in the parent
menu item would be meaningless because menu-bar-replace-menu is
not a command.
If you wanted to attach the same replace menu to a mouse click, you can do it this way:
(define-key global-map [C-S-down-mouse-1]
menu-bar-replace-menu)
Most window systems allow each frame to have a menu bar—a
permanently displayed menu stretching horizontally across the top of
the frame. (In order for a frame to display a menu bar, its
menu-bar-lines parameter must be greater than zero.
See Layout Parameters.)
The items of the menu bar are the subcommands of the fake “function
key” menu-bar, as defined in the active keymaps.
To add an item to the menu bar, invent a fake “function key” of your
own (let's call it key), and make a binding for the key sequence
[menu-bar key]. Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same fake function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined menu containing all the subcommands of that item—the global subcommands, the local subcommands, and the minor mode subcommands.
The variable overriding-local-map is normally ignored when
determining the menu bar contents. That is, the menu bar is computed
from the keymaps that would be active if overriding-local-map
were nil. See Active Keymaps.
Here's an example of setting up a menu bar item:
(modify-frame-parameters (selected-frame)
'((menu-bar-lines . 2)))
;; Make a menu keymap (with a prompt string)
;; and make it the menu bar item's definition.
(define-key global-map [menu-bar words]
(cons "Words" (make-sparse-keymap "Words")))
;; Define specific subcommands in this menu.
(define-key global-map
[menu-bar words forward]
'("Forward word" . forward-word))
(define-key global-map
[menu-bar words backward]
'("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by
rebinding the same fake function key with undefined as the
binding. For example, this is how Dired suppresses the ‘Edit’ menu
bar item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
Here, edit is the fake function key used by the global map for
the ‘Edit’ menu bar item. The main reason to suppress a global
menu bar item is to regain space for mode-specific items.
Normally the menu bar shows global items followed by items defined by the local maps.
This variable holds a list of fake function keys for items to display at the end of the menu bar rather than in normal sequence. The default value is
(help-menu); thus, the ‘Help’ menu item normally appears at the end of the menu bar, following local menu items.
This normal hook is run by redisplay to update the menu bar contents, before redisplaying the menu bar. You can use it to update submenus whose contents should vary. Since this hook is run frequently, we advise you to ensure that the functions it calls do not take much time in the usual case.
Next to every menu bar item, Emacs displays a key binding that runs
the same command (if such a key binding exists). This serves as a
convenient hint for users who do not know the key binding. If a
command has multiple bindings, Emacs normally displays the first one
it finds. You can specify one particular key binding by assigning an
:advertised-binding symbol property to the command. For
instance, the following tells Emacs to show C-/ for the
undo menu item:
(put 'undo :advertised-binding [?\C-/])
If the :advertised-binding property specifies a key binding
that the command does not actually have, it is ignored.
A tool bar is a row of icons at the top of a frame, that execute commands when you click on them—in effect, a kind of graphical menu bar.
The frame parameter tool-bar-lines (X resource ‘toolBar’)
controls how many lines' worth of height to reserve for the tool bar. A
zero value suppresses the tool bar. If the value is nonzero, and
auto-resize-tool-bars is non-nil, the tool bar expands and
contracts automatically as needed to hold the specified contents.
If the value of auto-resize-tool-bars is grow-only,
the tool bar expands automatically, but does not contract automatically.
To contract the tool bar, the user has to redraw the frame by entering
C-l.
The tool bar contents are controlled by a menu keymap attached to a
fake “function key” called tool-bar (much like the way the menu
bar is controlled). So you define a tool bar item using
define-key, like this:
(define-key global-map [tool-bar key] item)
where key is a fake “function key” to distinguish this item from other items, and item is a menu item key binding (see Extended Menu Items), which says how to display this item and how it behaves.
The usual menu keymap item properties, :visible,
:enable, :button, and :filter, are useful in
tool bar bindings and have their normal meanings. The real-binding
in the item must be a command, not a keymap; in other words, it does not
work to define a tool bar icon as a prefix key.
The :help property specifies a “help-echo” string to display
while the mouse is on that item. This is displayed in the same way as
help-echo text properties (see Help display).
In addition, you should use the :image property;
this is how you specify the image to display in the tool bar:
:image imageIf image is a single image specification, Emacs draws the tool bar button in disabled state by applying an edge-detection algorithm to the image.
The :rtl property specifies an alternative image to use for
right-to-left languages. Only the Gtk+ version of Emacs supports this
at present.
The default tool bar is defined so that items specific to editing do not
appear for major modes whose command symbol has a mode-class
property of special (see Major Mode Conventions). Major
modes may add items to the global bar by binding [tool-bar
foo] in their local map. It makes sense for some major modes to
replace the default tool bar items completely, since not many can be
accommodated conveniently, and the default bindings make this easy by
using an indirection through tool-bar-map.
By default, the global map binds
[tool-bar]as follows:(global-set-key [tool-bar] '(menu-item "tool bar" ignore :filter (lambda (ignore) tool-bar-map)))Thus the tool bar map is derived dynamically from the value of variable
tool-bar-mapand you should normally adjust the default (global) tool bar by changing that map. Major modes may replace the global bar completely by makingtool-bar-mapbuffer-local and set to a keymap containing only the desired items. Info mode provides an example.
There are two convenience functions for defining tool bar items, as follows.
This function adds an item to the tool bar by modifying
tool-bar-map. The image to use is defined by icon, which is the base name of an XPM, XBM or PBM image file to be located byfind-image. Given a value ‘"exit"’, say, exit.xpm, exit.pbm and exit.xbm would be searched for in that order on a color display. On a monochrome display, the search order is ‘.pbm’, ‘.xbm’ and ‘.xpm’. The binding to use is the command def, and key is the fake function key symbol in the prefix keymap. The remaining arguments props are additional property list elements to add to the menu item specification.To define items in some local map, bind
tool-bar-mapwithletaround calls of this function:(defvar foo-tool-bar-map (let ((tool-bar-map (make-sparse-keymap))) (tool-bar-add-item ...) ... tool-bar-map))
This function is a convenience for defining tool bar items which are consistent with existing menu bar bindings. The binding of command is looked up in the menu bar in map (default
global-map) and modified to add an image specification for icon, which is found in the same way as bytool-bar-add-item. The resulting binding is then placed intool-bar-map, so use this function only for global tool bar items.map must contain an appropriate keymap bound to
[menu-bar]. The remaining arguments props are additional property list elements to add to the menu item specification.
This function is used for making non-global tool bar items. Use it like
tool-bar-add-item-from-menuexcept that in-map specifies the local map to make the definition in. The argument from-map is like the map argument oftool-bar-add-item-from-menu.
If this variable is non-
nil, the tool bar automatically resizes to show all defined tool bar items—but not larger than a quarter of the frame's height.If the value is
grow-only, the tool bar expands automatically, but does not contract automatically. To contract the tool bar, the user has to redraw the frame by entering C-l.If Emacs is built with GTK or Nextstep, the tool bar can only show one line, so this variable has no effect.
If this variable is non-
nil, tool bar items display in raised form when the mouse moves over them.
This variable specifies an extra margin to add around tool bar items. The value is an integer, a number of pixels. The default is 4.
This variable specifies the shadow width for tool bar items. The value is an integer, a number of pixels. The default is 1.
This variable specifies the height of the border drawn below the tool bar area. An integer value specifies height as a number of pixels. If the value is one of
internal-border-width(the default) orborder-width, the tool bar border height corresponds to the corresponding frame parameter.
You can define a special meaning for clicking on a tool bar item with the shift, control, meta, etc., modifiers. You do this by setting up additional items that relate to the original item through the fake function keys. Specifically, the additional items should use the modified versions of the same fake function key used to name the original item.
Thus, if the original item was defined this way,
(define-key global-map [tool-bar shell]
'(menu-item "Shell" shell
:image (image :type xpm :file "shell.xpm")))
then here is how you can define clicking on the same tool bar image with the shift modifier:
(define-key global-map [tool-bar S-shell] 'some-command)
See Function Keys, for more information about how to add modifiers to function keys.
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use define-key to add the item, it normally goes at the front of
the menu. To put it elsewhere in the menu, use define-key-after:
Define a binding in map for key, with value binding, just like
define-key, but position the binding in map after the binding for the event after. The argument key should be of length one—a vector or string with just one element. But after should be a single event type—a symbol or a character, not a sequence. The new binding goes after the binding for after. If after istor is omitted, then the new binding goes last, at the end of the keymap. However, new bindings are added before any inherited keymap.Here is an example:
(define-key-after my-menu [drink] '("Drink" . drink-command) 'eat)makes a binding for the fake function key <DRINK> and puts it right after the binding for <EAT>.
Here is how to insert an item called ‘Work’ in the ‘Signals’ menu of Shell mode, after the item
break:(define-key-after (lookup-key shell-mode-map [menu-bar signals]) [work] '("Work" . work-command) 'break)
A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.
This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see Keymaps, and Syntax Tables.
A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides hooks for the sake of customization. Most often, hooks are set up in the init file (see Init File), but Lisp programs can set them also. See Standard Hooks, for a list of standard hook variables.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. By convention, whenever the hook name ends in ‘-hook’, that tells you it is normal. We try to make all hooks normal, as much as possible, so that you can use them in a uniform way.
Every major mode function is supposed to run a normal hook called
the mode hook as the one of the last steps of initialization.
This makes it easy for a user to customize the behavior of the mode,
by overriding the buffer-local variable assignments already made by
the mode. Most minor mode functions also run a mode hook at the end.
But hooks are used in other contexts too. For example, the hook
suspend-hook runs just before Emacs suspends itself
(see Suspending Emacs).
The recommended way to add a hook function to a normal hook is by
calling add-hook (see below). The hook functions may be any of
the valid kinds of functions that funcall accepts (see What Is a Function). Most normal hook variables are initially void;
add-hook knows how to deal with this. You can add hooks either
globally or buffer-locally with add-hook.
If the hook variable's name does not end with ‘-hook’, that
indicates it is probably an abnormal hook. That means the hook
functions are called with arguments, or their return values are used
in some way. The hook's documentation says how the functions are
called. You can use add-hook to add a function to an abnormal
hook, but you must write the function to follow the hook's calling
convention.
By convention, abnormal hook names end in ‘-functions’ or ‘-hooks’. If the variable's name ends in ‘-function’, then its value is just a single function, not a list of functions.
At the appropriate times, Emacs uses the run-hooks function
and the other functions below to run particular hooks.
This function takes one or more normal hook variable names as arguments, and runs each hook in turn. Each argument should be a symbol that is a normal hook variable. These arguments are processed in the order specified.
If a hook variable has a non-
nilvalue, that value should be a list of functions.run-hookscalls all the functions, one by one, with no arguments.The hook variable's value can also be a single function—either a lambda expression or a symbol with a function definition—which
run-hookscalls. But this usage is obsolete.
This function is the way to run an abnormal hook and always call all of the hook functions. It calls each of the hook functions one by one, passing each of them the arguments args.
This function is the way to run an abnormal hook until one of the hook functions fails. It calls each of the hook functions, passing each of them the arguments args, until some hook function returns
nil. It then stops and returnsnil. If none of the hook functions returnnil, it returns a non-nilvalue.
This function is the way to run an abnormal hook until a hook function succeeds. It calls each of the hook functions, passing each of them the arguments args, until some hook function returns non-
nil. Then it stops, and returns whatever was returned by the last hook function that was called. If all hook functions returnnil, it returnsnilas well.
Here's an example that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode:
(add-hook 'lisp-interaction-mode-hook 'turn-on-auto-fill)
This function is the handy way to add function function to hook variable hook. You can use it for abnormal hooks as well as for normal hooks. function can be any Lisp function that can accept the proper number of arguments for hook. For example,
(add-hook 'text-mode-hook 'my-text-hook-function)adds
my-text-hook-functionto the hook calledtext-mode-hook.If function is already present in hook (comparing using
equal), thenadd-hookdoes not add it a second time.If function has a non-
nilpropertypermanent-local-hook, thenkill-all-local-variables(or changing major modes) won't delete it from the hook variable's local value.It is best to design your hook functions so that the order in which they are executed does not matter. Any dependence on the order is asking for trouble. However, the order is predictable: normally, function goes at the front of the hook list, so it will be executed first (barring another
add-hookcall). If the optional argument append is non-nil, the new hook function goes at the end of the hook list and will be executed last.
add-hookcan handle the cases where hook is void or its value is a single function; it sets or changes the value to a list of functions.If local is non-
nil, that says to add function to the buffer-local hook list instead of to the global hook list. If needed, this makes the hook buffer-local and addstto the buffer-local value. The latter acts as a flag to run the hook functions in the default value as well as in the local value.
This function removes function from the hook variable hook. It compares function with elements of hook using
equal, so it works for both symbols and lambda expressions.If local is non-
nil, that says to remove function from the buffer-local hook list instead of from the global hook list.
Major modes specialize Emacs for editing particular kinds of text. Each buffer has only one major mode at a time. For each major mode there is a function to switch to that mode in the current buffer; its name should end in ‘-mode’. These functions work by setting buffer-local variable bindings and other data associated with the buffer, such as a local keymap. The effect lasts until you switch to another major mode in the same buffer.
The least specialized major mode is called Fundamental mode.
This mode has no mode-specific definitions or variable settings, so each
Emacs command behaves in its default manner, and each option is in its
default state. All other major modes redefine various keys and options.
For example, Lisp Interaction mode provides special key bindings for
C-j (eval-print-last-sexp), <TAB>
(lisp-indent-line), and other keys.
When you need to write several editing commands to help you perform a specialized editing task, creating a new major mode is usually a good idea. In practice, writing a major mode is easy (in contrast to writing a minor mode, which is often difficult).
If the new mode is similar to an old one, it is often unwise to
modify the old one to serve two purposes, since it may become harder
to use and maintain. Instead, copy and rename an existing major mode
definition and alter the copy—or use the define-derived-mode
macro to define a derived mode (see Derived Modes). For
example, Rmail Edit mode is a major mode that is very similar to Text
mode except that it provides two additional commands. Its definition
is distinct from that of Text mode, but uses that of Text mode.
Even if the new mode is not an obvious derivative of any other mode,
we recommend to use define-derived-mode, since it automatically
enforces the most important coding conventions for you.
For a very simple programming language major mode that handles
comments and fontification, you can use define-generic-mode.
See Generic Modes.
Rmail Edit mode offers an example of changing the major mode temporarily for a buffer, so it can be edited in a different way (with ordinary Emacs commands rather than Rmail commands). In such cases, the temporary major mode usually provides a command to switch back to the buffer's usual mode (Rmail mode, in this case). You might be tempted to present the temporary redefinitions inside a recursive edit and restore the usual ones when the user exits; but this is a bad idea because it constrains the user's options when it is done in more than one buffer: recursive edits must be exited most-recently-entered first. Using an alternative major mode avoids this limitation. See Recursive Editing.
The standard GNU Emacs Lisp library directory tree contains the code for several major modes, in files such as text-mode.el, texinfo.el, lisp-mode.el, c-mode.el, and rmail.el. They are found in various subdirectories of the lisp directory. You can study these libraries to see how modes are written. Text mode is perhaps the simplest major mode aside from Fundamental mode. Rmail mode is a complicated and specialized mode.
The code for existing major modes follows various coding conventions, including conventions for local keymap and syntax table initialization, global names, and hooks. Please follow these conventions when you define a new major mode. (Fundamental mode is an exception to many of these conventions, because its definition is to present the global state of Emacs.)
This list of conventions is only partial, because each major mode should aim for consistency in general with other Emacs major modes. This makes Emacs as a whole more coherent. It is impossible to list here all the possible points where this issue might come up; if the Emacs developers point out an area where your major mode deviates from the usual conventions, please make it compatible.
describe-mode) in your mode will display this string.
The documentation string may include the special documentation substrings, ‘\[command]’, ‘\{keymap}’, and ‘\<keymap>’, which enable the documentation to adapt automatically to the user's own key bindings. See Keys in Documentation.
kill-all-local-variables. This runs the normal hook
change-major-mode-hook, then gets rid of the buffer-local
variables of the major mode previously in effect. See Creating Buffer-Local.
major-mode to the
major mode command symbol. This is how describe-mode discovers
which documentation to print.
mode-name to the
“pretty” name of the mode, usually a string (but see Mode Line Data, for other possible forms). The name of the mode appears
in the mode line.
indent-line-function
to a suitable function, and probably customize other variables
for indentation. See Auto-Indentation.
use-local-map to install this local map. See Active Keymaps, for more information.
This keymap should be stored permanently in a global variable named
modename-mode-map. Normally the library that defines the
mode sets this variable.
See Tips for Defining, for advice about how to write the code to set up the mode's keymap variable.
A major mode can also rebind the keys M-n, M-p and M-s. The bindings for M-n and M-p should normally be some kind of “moving forward and backward,” but this does not necessarily mean cursor motion.
It is legitimate for a major mode to rebind a standard key sequence if it provides a command that does “the same job” in a way better suited to the text this mode is used for. For example, a major mode for editing a programming language might redefine C-M-a to “move to the beginning of a function” in a way that works better for that language.
It is also legitimate for a major mode to rebind a standard key sequence whose standard meaning is rarely useful in that mode. For instance, minibuffer modes rebind M-r, whose standard meaning is rarely of any use in the minibuffer. Major modes such as Dired or Rmail that do not allow self-insertion of text can reasonably redefine letters and other printing characters as special commands.
-mode-syntax-table. See Syntax Tables.
-mode-abbrev-table. If the
major mode command defines any abbrevs itself, it should pass t
for the system-flag argument to define-abbrev.
See Defining Abbrevs.
font-lock-defaults (see Font Lock Mode).
imenu-generic-expression, for the two variables
imenu-prev-index-position-function and
imenu-extract-index-name-function, or for the variable
imenu-create-index-function (see Imenu).
eldoc-documentation-function to tell ElDoc mode how to handle
this mode.
completion-at-point-functions.
defvar or defcustom to set mode-related variables, so
that they are not reinitialized if they already have a value. (Such
reinitialization could discard customizations made by the user.)
make-local-variable in the major mode command, not
make-variable-buffer-local. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See Buffer-Local Variables.
With rare exceptions, the only reasonable way to use
make-variable-buffer-local in a Lisp package is for a variable
which is used only within that package. Using it on a variable used by
other packages would interfere with them.
-mode-hook. The very last thing the major mode command
should do is to call run-mode-hooks. This runs the mode hook,
and then runs the normal hook after-change-major-mode-hook.
See Mode Hooks.
define-derived-mode
macro, but this is not required. Such a mode should call the parent
mode command inside a delay-mode-hooks form. (Using
define-derived-mode does this automatically.) See Derived Modes, and Mode Hooks.
change-major-mode-hook (see Creating Buffer-Local).
mode-class
with value special, put on as follows:
(put 'funny-mode 'mode-class 'special)
This tells Emacs that new buffers created while the current buffer is
in Funny mode should not inherit Funny mode, in case the default value
of major-mode is nil. Modes such as Dired, Rmail,
and Buffer List use this feature.
The define-derived-mode macro automatically marks the derived
mode as special if the parent mode is special. The special mode
special-mode provides a convenient parent for other special
modes to inherit from; it sets buffer-read-only to t,
and does little else.
auto-mode-alist to select
the mode for those file names (see Auto Major Mode). If you
define the mode command to autoload, you should add this element in
the same file that calls autoload. If you use an autoload
cookie for the mode command, you can also use an autoload cookie for
the form that adds the element (see autoload cookie). If you do
not autoload the mode command, it is sufficient to add the element in
the file that contains the mode definition.
autoload form and an example of how to add to
auto-mode-alist, that users can include in their init files
(see Init File).
Based on information in the file name or in the file itself, Emacs automatically selects a major mode for the new buffer when a file is visited. It also processes local variables specified in the file text.
Fundamental mode is a major mode that is not specialized for anything in particular. Other major modes are defined in effect by comparison with this one—their definitions say what to change, starting from Fundamental mode. The
fundamental-modefunction does not run any mode hooks; you're not supposed to customize it. (If you want Emacs to behave differently in Fundamental mode, change the global state of Emacs.)
This function establishes the proper major mode and buffer-local variable bindings for the current buffer. First it calls
set-auto-mode(see below), then it runshack-local-variablesto parse, and bind or evaluate as appropriate, the file's local variables (see File Local Variables).If the find-file argument to
normal-modeis non-nil,normal-modeassumes that thefind-filefunction is calling it. In this case, it may process local variables in the ‘-*-’ line or at the end of the file. The variableenable-local-variablescontrols whether to do so. See Local Variables in Files, for the syntax of the local variables section of a file.If you run
normal-modeinteractively, the argument find-file is normallynil. In this case,normal-modeunconditionally processes any file local variables.If
normal-modeprocesses the local variables list and this list specifies a major mode, that mode overrides any mode chosen byset-auto-mode. If neitherset-auto-modenorhack-local-variablesspecify a major mode, the buffer stays in the major mode determined by the default value ofmajor-mode(see below).
normal-modeusescondition-casearound the call to the major mode function, so errors are caught and reported as a ‘File mode specification error’, followed by the original error message.
This function selects the major mode that is appropriate for the current buffer. It bases its decision (in order of precedence) on the ‘-*-’ line, on the ‘#!’ line (using
interpreter-mode-alist), on the text at the beginning of the buffer (usingmagic-mode-alist), and finally on the visited file name (usingauto-mode-alist). See How Major Modes are Chosen. However, this function does not look for the ‘mode:’ local variable near the end of a file; thehack-local-variablesfunction does that. Ifenable-local-variablesisnil,set-auto-modedoes not check the ‘-*-’ line for a mode tag either.If keep-mode-if-same is non-
nil, this function does not call the mode command if the buffer is already in the proper major mode. For instance,set-visited-file-namesets this totto avoid killing buffer local variables that the user may have set.
The buffer-local value of this variable holds the major mode currently active. The default value of this variable holds the default major mode for new buffers. The standard default value is
fundamental-mode.If the default value of
major-modeisnil, Emacs uses the (previously) current buffer's major mode as the default major mode of a new buffer. However, if that major mode symbol has amode-classproperty with valuespecial, then it is not used for new buffers; Fundamental mode is used instead. The modes that have this property are those such as Dired and Rmail that are useful only with text that has been specially prepared.
This function sets the major mode of buffer to the default value of
major-mode; if that isnil, it uses the current buffer's major mode (if that is suitable). As an exception, if buffer's name is ‘*scratch*’, it sets the mode toinitial-major-mode.The low-level primitives for creating buffers do not use this function, but medium-level commands such as
switch-to-bufferandfind-file-noselectuse it whenever they create buffers.
The value of this variable determines the major mode of the initial ‘*scratch*’ buffer. The value should be a symbol that is a major mode command. The default value is
lisp-interaction-mode.
This variable specifies major modes to use for scripts that specify a command interpreter in a ‘#!’ line. Its value is an alist with elements of the form
(interpreter.mode); for example,("perl" . perl-mode)is one element present by default. The element says to use mode mode if the file specifies an interpreter which matches interpreter.
This variable's value is an alist with elements of the form
(regexp.function), where regexp is a regular expression and function is a function ornil. After visiting a file,set-auto-modecalls function if the text at the beginning of the buffer matches regexp and function is non-nil; if function isnil,auto-mode-alistgets to decide the mode.
This works like
magic-mode-alist, except that it is handled only ifauto-mode-alistdoes not specify a mode for this file.
This variable contains an association list of file name patterns (regular expressions) and corresponding major mode commands. Usually, the file name patterns test for suffixes, such as ‘.el’ and ‘.c’, but this need not be the case. An ordinary element of the alist looks like
(regexp.mode-function).For example,
(("\\`/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode) ("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) ...)When you visit a file whose expanded file name (see File Name Expansion), with version numbers and backup suffixes removed using
file-name-sans-versions(see File Name Components), matches a regexp,set-auto-modecalls the corresponding mode-function. This feature enables Emacs to select the proper major mode for most files.If an element of
auto-mode-alisthas the form(regexp functiont), then after calling function, Emacs searchesauto-mode-alistagain for a match against the portion of the file name that did not match before. This feature is useful for uncompression packages: an entry of the form("\\.gz\\'"functiont)can uncompress the file and then put the uncompressed file in the proper mode according to the name sans ‘.gz’.Here is an example of how to prepend several pattern pairs to
auto-mode-alist. (You might use this sort of expression in your init file.)(setq auto-mode-alist (append ;; File name (within directory) starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("/[^\\./]*\\'" . fundamental-mode) ;; File name ends in ‘.C’. ("\\.C\\'" . c++-mode)) auto-mode-alist))
The describe-mode function is used to provide information
about major modes. It is normally called with C-h m. The
describe-mode function uses the value of major-mode,
which is why every major mode function needs to set the
major-mode variable.
This function displays the documentation of the current major mode.
The
describe-modefunction calls thedocumentationfunction using the value ofmajor-modeas an argument. Thus, it displays the documentation string of the major mode function. (See Accessing Documentation.)
This buffer-local variable holds the symbol for the current buffer's major mode. This symbol should have a function definition that is the command to switch to that major mode. The
describe-modefunction uses the documentation string of the function as the documentation of the major mode.
The recommended way to define a new major mode is to derive it
from an existing one using define-derived-mode. If there is no
closely related mode, you can inherit from text-mode,
special-mode, or in the worst case fundamental-mode.
This macro defines variant as a major mode command, using name as the string form of the mode name. variant and parent should be unquoted symbols.
The new command variant is defined to call the function parent, then override certain aspects of that parent mode:
- The new mode has its own sparse keymap, named variant
-map.define-derived-modemakes the parent mode's keymap the parent of the new map, unless variant-mapis already set and already has a parent.- The new mode has its own syntax table, kept in the variable variant
-syntax-table, unless you override this using the:syntax-tablekeyword (see below).define-derived-modemakes the parent mode's syntax-table the parent of variant-syntax-table, unless the latter is already set and already has a parent different from the standard syntax table.- The new mode has its own abbrev table, kept in the variable variant
-abbrev-table, unless you override this using the:abbrev-tablekeyword (see below).- The new mode has its own mode hook, variant
-hook. It runs this hook, after running the hooks of its ancestor modes, withrun-mode-hooks, as the last thing it does. See Mode Hooks.In addition, you can specify how to override other aspects of parent with body. The command variant evaluates the forms in body after setting up all its usual overrides, just before running the mode hooks.
If parent has a non-
nilmode-classsymbol property, thendefine-derived-modesets themode-classproperty of variant to the same value. This ensures, for example, that if parent is a special mode, then variant is also a special mode (see Major Mode Conventions).You can also specify
nilfor parent. This gives the new mode no parent. Thendefine-derived-modebehaves as described above, but, of course, omits all actions connected with parent.The argument docstring specifies the documentation string for the new mode.
define-derived-modeadds some general information about the mode's hook, followed by the mode's keymap, at the end of this docstring. If you omit docstring,define-derived-modegenerates a documentation string.The keyword-args are pairs of keywords and values. The values are evaluated. The following keywords are currently supported:
:syntax-table- You can use this to explicitly specify a syntax table for the new mode. If you specify a
nilvalue, the new mode uses the same syntax table as parent, or the standard syntax table if parent isnil. (Note that this does not follow the convention used for non-keyword arguments that anilvalue is equivalent with not specifying the argument.):abbrev-table- You can use this to explicitly specify an abbrev table for the new mode. If you specify a
nilvalue, the new mode uses the same abbrev table as parent, orfundamental-mode-abbrev-tableif parent isnil. (Again, anilvalue is not equivalent to not specifying this keyword.):group- If this is specified, the value should be the customization group for this mode. (Not all major modes have one.) Only the (still experimental and unadvertised) command
customize-modecurrently uses this.define-derived-modedoes not automatically define the specified customization group.Here is a hypothetical example:
(define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)Do not write an
interactivespec in the definition;define-derived-modedoes that automatically.
Generic modes are simple major modes with basic support for
comment syntax and Font Lock mode. To define a generic mode, use the
macro define-generic-mode. See the file generic-x.el
for some examples of the use of define-generic-mode.
This macro defines a generic mode command named mode (a symbol, not quoted). The optional argument docstring is the documentation for the mode command. If you do not supply it,
define-generic-modegenerates one by default.The argument comment-list is a list in which each element is either a character, a string of one or two characters, or a cons cell. A character or a string is set up in the mode's syntax table as a “comment starter.” If the entry is a cons cell, the car is set up as a “comment starter” and the cdr as a “comment ender.” (Use
nilfor the latter if you want comments to end at the end of the line.) Note that the syntax table mechanism has limitations about what comment starters and enders are actually possible. See Syntax Tables.The argument keyword-list is a list of keywords to highlight with
font-lock-keyword-face. Each keyword should be a string. Meanwhile, font-lock-list is a list of additional expressions to highlight. Each element of this list should have the same form as an element offont-lock-keywords. See Search-based Fontification.The argument auto-mode-list is a list of regular expressions to add to the variable
auto-mode-alist. They are added by the execution of thedefine-generic-modeform, not by expanding the macro call.Finally, function-list is a list of functions for the mode command to call for additional setup. It calls these functions just before it runs the mode hook variable mode
-hook.
Every major mode function should finish by running its mode hook and
the mode-independent normal hook after-change-major-mode-hook.
It does this by calling run-mode-hooks. If the major mode is a
derived mode, that is if it calls another major mode (the parent mode)
in its body, it should do this inside delay-mode-hooks so that
the parent won't run these hooks itself. Instead, the derived mode's
call to run-mode-hooks runs the parent's mode hook too.
See Major Mode Conventions.
Emacs versions before Emacs 22 did not have delay-mode-hooks.
When user-implemented major modes have not been updated to use it,
they won't entirely follow these conventions: they may run the
parent's mode hook too early, or fail to run
after-change-major-mode-hook. If you encounter such a major
mode, please correct it to follow these conventions.
When you defined a major mode using define-derived-mode, it
automatically makes sure these conventions are followed. If you
define a major mode “by hand,” not using define-derived-mode,
use the following functions to handle these conventions automatically.
Major modes should run their mode hook using this function. It is similar to
run-hooks(see Hooks), but it also runsafter-change-major-mode-hook.When this function is called during the execution of a
delay-mode-hooksform, it does not run the hooks immediately. Instead, it arranges for the next call torun-mode-hooksto run them.
When one major mode command calls another, it should do so inside of
delay-mode-hooks.This macro executes body, but tells all
run-mode-hookscalls during the execution of body to delay running their hooks. The hooks will actually run during the next call torun-mode-hooksafter the end of thedelay-mode-hooksconstruct.
This is a normal hook run by
run-mode-hooks. It is run at the very end of every properly-written major mode function.
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from text-mode.el that illustrate many of the conventions listed above:
;; Create the syntax table for this mode. (defvar text-mode-syntax-table (let ((st (make-syntax-table))) (modify-syntax-entry ?\" ". " st) (modify-syntax-entry ?\\ ". " st) ;; Add `p' so M-c on `hello' leads to `Hello', not `hello'. (modify-syntax-entry ?' "w p" st) st) "Syntax table used while in `text-mode'.") ;; Create the keymap for this mode. (defvar text-mode-map (let ((map (make-sparse-keymap))) (define-key map "\e\t" 'ispell-complete-word) (define-key map "\es" 'center-line) (define-key map "\eS" 'center-paragraph) map) "Keymap for `text-mode'. Many other modes, such as Mail mode, Outline mode and Indented Text mode, inherit all the commands defined in this map.")
Here is how the actual mode command is defined now:
(define-derived-mode text-mode nil "Text"
"Major mode for editing text written for humans to read.
In this mode, paragraphs are delimited only by blank or white lines.
You can thus get the full benefit of adaptive filling
(see the variable `adaptive-fill-mode').
\\{text-mode-map}
Turning on Text mode runs the normal hook `text-mode-hook'."
(set (make-local-variable 'text-mode-variant) t)
;; These two lines are a feature added recently.
(set (make-local-variable 'require-final-newline)
mode-require-final-newline)
(set (make-local-variable 'indent-line-function) 'indent-relative))
(The last line is redundant nowadays, since indent-relative is
the default value, and we'll delete it in a future version.)
Here is how it was defined formerly, before
define-derived-mode existed:
;; This isn't needed nowadays, since define-derived-mode does it.
(define-abbrev-table 'text-mode-abbrev-table ()
"Abbrev table used while in text mode.")
(defun text-mode ()
"Major mode for editing text intended for humans to read...
Special commands: \\{text-mode-map}
Turning on text-mode runs the hook `text-mode-hook'."
(interactive)
(kill-all-local-variables)
(use-local-map text-mode-map)
(setq local-abbrev-table text-mode-abbrev-table)
(set-syntax-table text-mode-syntax-table)
;; These four lines are absent from the current version
;; not because this is done some other way, but rather
;; because nowadays Text mode uses the normal definition of paragraphs.
(set (make-local-variable 'paragraph-start)
(concat "[ \t]*$\\|" page-delimiter))
(set (make-local-variable 'paragraph-separate) paragraph-start)
(set (make-local-variable 'indent-line-function) 'indent-relative-maybe)
(setq mode-name "Text")
(setq major-mode 'text-mode)
(run-mode-hooks 'text-mode-hook)) ; Finally, this permits the user to
; customize the mode with a hook.
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from lisp-mode.el that illustrate how these modes are written.
;; Create mode-specific table variables.
(defvar lisp-mode-syntax-table nil "")
(defvar lisp-mode-abbrev-table nil "")
(defvar emacs-lisp-mode-syntax-table
(let ((table (make-syntax-table)))
(let ((i 0))
;; Set syntax of chars up to ‘0’ to say they are
;; part of symbol names but not words.
;; (The digit ‘0’ is 48 in the ASCII character set.)
(while (< i ?0)
(modify-syntax-entry i "_ " table)
(setq i (1+ i)))
;; ... similar code follows for other character ranges.
;; Then set the syntax codes for characters that are special in Lisp.
(modify-syntax-entry ? " " table)
(modify-syntax-entry ?\t " " table)
(modify-syntax-entry ?\f " " table)
(modify-syntax-entry ?\n "> " table)
;; Give CR the same syntax as newline, for selective-display.
(modify-syntax-entry ?\^m "> " table)
(modify-syntax-entry ?\; "< " table)
(modify-syntax-entry ?` "' " table)
(modify-syntax-entry ?' "' " table)
(modify-syntax-entry ?, "' " table)
;; ...likewise for many other characters...
(modify-syntax-entry ?\( "() " table)
(modify-syntax-entry ?\) ")( " table)
(modify-syntax-entry ?\[ "(] " table)
(modify-syntax-entry ?\] ")[ " table))
table))
;; Create an abbrev table for lisp-mode.
(define-abbrev-table 'lisp-mode-abbrev-table ())
The three modes for Lisp share much of their code. For instance, each calls the following function to set various variables:
(defun lisp-mode-variables (lisp-syntax)
(when lisp-syntax
(set-syntax-table lisp-mode-syntax-table))
(setq local-abbrev-table lisp-mode-abbrev-table)
...
In Lisp and most programming languages, we want the paragraph
commands to treat only blank lines as paragraph separators. And the
modes should understand the Lisp conventions for comments. The rest of
lisp-mode-variables sets this up:
(set (make-local-variable 'paragraph-start) (concat page-delimiter "\\|$" ))
(set (make-local-variable 'paragraph-separate) paragraph-start)
...
(set (make-local-variable 'comment-indent-function) 'lisp-comment-indent))
...
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-z to run-lisp, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following code sets up the common commands:
(defvar shared-lisp-mode-map
(let ((map (make-sparse-keymap)))
(define-key shared-lisp-mode-map "\e\C-q" 'indent-sexp)
(define-key shared-lisp-mode-map "\177"
'backward-delete-char-untabify)
map)
"Keymap for commands shared by all sorts of Lisp modes.")
And here is the code to set up the keymap for Lisp mode:
(defvar lisp-mode-map
(let ((map (make-sparse-keymap)))
(set-keymap-parent map shared-lisp-mode-map)
(define-key map "\e\C-x" 'lisp-eval-defun)
(define-key map "\C-c\C-z" 'run-lisp)
map)
"Keymap for ordinary Lisp mode...")
Finally, here is the complete major mode function definition for Lisp mode.
(defun lisp-mode ()
"Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{lisp-mode-map}
Note that `run-lisp' may be used either to start an inferior Lisp job
or to switch back to an existing one.
Entry to this mode calls the value of `lisp-mode-hook'
if that value is non-nil."
(interactive)
(kill-all-local-variables)
(use-local-map lisp-mode-map) ; Select the mode's keymap.
(setq major-mode 'lisp-mode) ; This is how describe-mode
; finds out what to describe.
(setq mode-name "Lisp") ; This goes into the mode line.
(lisp-mode-variables t) ; This defines various variables.
(set (make-local-variable 'comment-start-skip)
"\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *")
(set (make-local-variable 'font-lock-keywords-case-fold-search) t)
(setq imenu-case-fold-search t)
(set-syntax-table lisp-mode-syntax-table)
(run-mode-hooks 'lisp-mode-hook)) ; This permits the user to use a
; hook to customize the mode.
A minor mode provides features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination. Minor modes would be better named “generally available, optional feature modes,” except that such a name would be unwieldy.
A minor mode is not usually meant as a variation of a single major mode. Usually they are general and can apply to many major modes. For example, Auto Fill mode works with any major mode that permits text insertion. To be general, a minor mode must be effectively independent of the things major modes do.
A minor mode is often much more difficult to implement than a major mode. One reason is that you should be able to activate and deactivate minor modes in any order. A minor mode should be able to have its desired effect regardless of the major mode and regardless of the other minor modes in effect.
Often the biggest problem in implementing a minor mode is finding a way to insert the necessary hook into the rest of Emacs. Minor mode keymaps make this easier than it used to be.
There are conventions for writing minor modes just as there are for major modes. Several of the major mode conventions apply to minor modes as well: those regarding the name of the mode initialization function, the names of global symbols, the use of a hook at the end of the initialization function, and the use of keymaps and other tables.
In addition, there are several conventions that are specific to
minor modes. (The easiest way to follow all the conventions is to use
the macro define-minor-mode; Defining Minor Modes.)
nil to disable; anything else to
enable).
If possible, implement the mode so that setting the variable automatically enables or disables the mode. Then the minor mode command does not need to do anything except set the variable.
This variable is used in conjunction with the minor-mode-alist to
display the minor mode name in the mode line. It can also enable
or disable a minor mode keymap. Individual commands or hooks can also
check the variable's value.
If you want the minor mode to be enabled separately in each buffer, make the variable buffer-local.
The command should accept one optional argument. If the argument is
nil, it should toggle the mode (turn it on if it is off, and
off if it is on). It should turn the mode on if the argument is a
positive integer, the symbol t, or a list whose car is one
of those. It should turn the mode off if the argument is a negative
integer or zero, the symbol -, or a list whose car is a
negative integer or zero. The meaning of other arguments is not
specified.
Here is an example taken from the definition of transient-mark-mode.
It shows the use of transient-mark-mode as a variable that enables or
disables the mode's behavior, and also shows the proper way to toggle,
enable or disable the minor mode based on the raw prefix argument value.
(setq transient-mark-mode
(if (null arg) (not transient-mark-mode)
(> (prefix-numeric-value arg) 0)))
minor-mode-alist for each minor mode
(see Definition of minor-mode-alist), if you want to indicate the
minor mode in the mode line. This element should be a list of the
following form:
(mode-variable string)
Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once.
When you add an element to minor-mode-alist, use assq to
check for an existing element, to avoid duplication. For example:
(unless (assq 'leif-mode minor-mode-alist)
(setq minor-mode-alist
(cons '(leif-mode " Leif") minor-mode-alist)))
or like this, using add-to-list (see List Variables):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Global minor modes distributed with Emacs should if possible support
enabling and disabling via Custom (see Customization). To do this,
the first step is to define the mode variable with defcustom, and
specify :type 'boolean.
If just setting the variable is not sufficient to enable the mode, you
should also specify a :set method which enables the mode by
invoking the mode command. Note in the variable's documentation string that
setting the variable other than via Custom may not take effect.
Also mark the definition with an autoload cookie (see autoload cookie),
and specify a :require so that customizing the variable will load
the library that defines the mode. This will copy suitable definitions
into loaddefs.el so that users can use customize-option to
enable the mode. For example:
;;;###autoload
(defcustom msb-mode nil
"Toggle msb-mode.
Setting this variable directly does not take effect;
use either \\[customize] or the function `msb-mode'."
:set 'custom-set-minor-mode
:initialize 'custom-initialize-default
:version "20.4"
:type 'boolean
:group 'msb
:require 'msb)
Each minor mode can have its own keymap, which is active when the mode
is enabled. To set up a keymap for a minor mode, add an element to the
alist minor-mode-map-alist. See Definition of minor-mode-map-alist.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. In general, this is the only way to do that, since the
facilities for customizing self-insert-command are limited to
special cases (designed for abbrevs and Auto Fill mode). (Do not try
substituting your own definition of self-insert-command for the
standard one. The editor command loop handles this function specially.)
The key sequences bound in a minor mode should consist of C-c followed by one of .,/?`'"[]\|~!#$%^&*()-_+=. (The other punctuation characters are reserved for major modes.)
The macro define-minor-mode offers a convenient way of
implementing a mode in one self-contained definition.
This macro defines a new minor mode whose name is mode (a symbol). It defines a command named mode to toggle the minor mode, with doc as its documentation string. It also defines a variable named mode, which is set to
tornilby enabling or disabling the mode. The variable is initialized to init-value. Except in unusual circumstances (see below), this value must benil.The string lighter says what to display in the mode line when the mode is enabled; if it is
nil, the mode is not displayed in the mode line.The optional argument keymap specifies the keymap for the minor mode. If non-
nil, it should be a variable name (whose value is a keymap), a keymap, or an alist of the form(key-sequence . definition)where each key-sequence and definition are arguments suitable for passing to
define-key(see Changing Key Bindings). If keymap is a keymap or an alist, this also defines the variable mode-map.The above three arguments init-value, lighter, and keymap can be (partially) omitted when keyword-args are used. The keyword-args consist of keywords followed by corresponding values. A few keywords have special meanings:
:groupgroup- Custom group name to use in all generated
defcustomforms. Defaults to mode without the possible trailing ‘-mode’. Warning: don't use this default group name unless you have written adefgroupto define that group properly. See Group Definitions.:globalglobal- If non-
nil, this specifies that the minor mode should be global rather than buffer-local. It defaults tonil.One of the effects of making a minor mode global is that the mode variable becomes a customization variable. Toggling it through the Custom interface turns the mode on and off, and its value can be saved for future Emacs sessions (see Saving Customizations. For the saved variable to work, you should ensure that the
define-minor-modeform is evaluated each time Emacs starts; for packages that are not part of Emacs, the easiest way to do this is to specify a:requirekeyword.:init-valueinit-value- This is equivalent to specifying init-value positionally.
:lighterlighter- This is equivalent to specifying lighter positionally.
:keymapkeymap- This is equivalent to specifying keymap positionally.
Any other keyword arguments are passed directly to the
defcustomgenerated for the variable mode.The command named mode first performs the standard actions such as setting the variable named mode and then executes the body forms, if any. It finishes by running the mode hook variable mode
-hook.
The initial value must be nil except in cases where (1) the
mode is preloaded in Emacs, or (2) it is painless for loading to
enable the mode even though the user did not request it. For
instance, if the mode has no effect unless something else is enabled,
and will always be loaded by that time, enabling it by default is
harmless. But these are unusual circumstances. Normally, the
initial value must be nil.
The name easy-mmode-define-minor-mode is an alias
for this macro.
Here is an example of using define-minor-mode:
(define-minor-mode hungry-mode
"Toggle Hungry mode.
With no argument, this command toggles the mode.
Non-null prefix argument turns on the mode.
Null prefix argument turns off the mode.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
nil
;; The indicator for the mode line.
" Hungry"
;; The minor mode bindings.
'(([C-backspace] . hungry-electric-delete))
:group 'hunger)
This defines a minor mode named “Hungry mode,” a command named
hungry-mode to toggle it, a variable named hungry-mode
which indicates whether the mode is enabled, and a variable named
hungry-mode-map which holds the keymap that is active when the
mode is enabled. It initializes the keymap with a key binding for
C-<DEL>. It puts the variable hungry-mode into
custom group hunger. There are no body forms—many
minor modes don't need any.
Here's an equivalent way to write it:
(define-minor-mode hungry-mode
"Toggle Hungry mode.
With no argument, this command toggles the mode.
Non-null prefix argument turns on the mode.
Null prefix argument turns off the mode.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
:init-value nil
;; The indicator for the mode line.
:lighter " Hungry"
;; The minor mode bindings.
:keymap
'(([C-backspace] . hungry-electric-delete)
([C-M-backspace]
. (lambda ()
(interactive)
(hungry-electric-delete t))))
:group 'hunger)
This defines a global toggle named global-mode whose meaning is to enable or disable the buffer-local minor mode mode in all buffers. To turn on the minor mode in a buffer, it uses the function turn-on; to turn off the minor mode, it calls
modewith −1 as argument.Globally enabling the mode also affects buffers subsequently created by visiting files, and buffers that use a major mode other than Fundamental mode; but it does not detect the creation of a new buffer in Fundamental mode.
This defines the customization option global-mode (see Customization), which can be toggled in the Custom interface to turn the minor mode on and off. As with
define-minor-mode, you should ensure that thedefine-globalized-minor-modeform is evaluated each time Emacs starts, for example by providing a:requirekeyword.Use
:groupgroup in keyword-args to specify the custom group for the mode variable of the global minor mode.
Each Emacs window (aside from minibuffer windows) typically has a mode line at the bottom, which displays status information about the buffer displayed in the window. The mode line contains information about the buffer, such as its name, associated file, depth of recursive editing, and major and minor modes. A window can also have a header line, which is much like the mode line but appears at the top of the window.
This section describes how to control the contents of the mode line and header line. We include it in this chapter because much of the information displayed in the mode line relates to the enabled major and minor modes.
mode-line-format is a buffer-local variable that holds a
mode line construct, a kind of template, which controls what is
displayed on the mode line of the current buffer. The value of
header-line-format specifies the buffer's header line in the
same way. All windows for the same buffer use the same
mode-line-format and header-line-format.
For efficiency, Emacs does not continuously recompute the mode
line and header line of a window. It does so when circumstances
appear to call for it—for instance, if you change the window
configuration, switch buffers, narrow or widen the buffer, scroll, or
change the buffer's modification status. If you modify any of the
variables referenced by mode-line-format (see Mode Line Variables), or any other variables and data structures that affect
how text is displayed (see Display), you may want to force an
update of the mode line so as to display the new information or
display it in the new way.
Force redisplay of the current buffer's mode line and header line. The next redisplay will update the mode line and header line based on the latest values of all relevant variables. With optional non-
nilall, force redisplay of all mode lines and header lines.This function also forces recomputation of the menu bar menus and the frame title.
The selected window's mode line is usually displayed in a different
color using the face mode-line. Other windows' mode lines
appear in the face mode-line-inactive instead. See Faces.
The mode-line contents are controlled by a data structure called a mode-line construct, made up of lists, strings, symbols, and numbers kept in buffer-local variables. Each data type has a specific meaning for the mode-line appearance, as described below. The same data structure is used for constructing frame titles (see Frame Titles) and header lines (see Header Lines).
A mode-line construct may be as simple as a fixed string of text, but it usually specifies how to combine fixed strings with variables' values to construct the text. Many of these variables are themselves defined to have mode-line constructs as their values.
Here are the meanings of various data types as mode-line constructs:
%-constructs in it. These stand for substitution of
other data; see %-Constructs.
If parts of the string have face properties, they control
display of the text just as they would text in the buffer. Any
characters which have no face properties are displayed, by
default, in the face mode-line or mode-line-inactive
(see Standard Faces). The
help-echo and local-map properties in string have
special meanings. See Properties in Mode.
t and nil are ignored, as is any
symbol whose value is void.
There is one exception: if the value of symbol is a string, it is
displayed verbatim: the %-constructs are not recognized.
Unless symbol is marked as “risky” (i.e., it has a
non-nil risky-local-variable property), all text
properties specified in symbol's value are ignored. This
includes the text properties of strings in symbol's value, as
well as all :eval and :propertize forms in it. (The
reason for this is security: non-risky variables could be set
automatically from file variables without prompting the user.)
(string rest...)(list rest...)(:eval form):eval says to evaluate
form, and use the result as a string to display. Make sure this
evaluation cannot load any files, as doing so could cause infinite
recursion.
(:propertize elt props...):propertize says to
process the mode-line construct elt recursively, then add the text
properties specified by props to the result. The argument
props should consist of zero or more pairs text-property
value. (This feature is new as of Emacs 22.1.)
(symbol then else)nil value, the second element,
then, is processed recursively as a mode-line element.
Otherwise, the third element, else, is processed recursively.
You may omit else; then the mode-line element displays nothing
if the value of symbol is nil or void.
(width rest...)For example, the usual way to show what percentage of a buffer is above
the top of the window is to use a list like this: (-3 "%p").
The variable in overall control of the mode line is
mode-line-format.
The value of this variable is a mode-line construct that controls the contents of the mode-line. It is always buffer-local in all buffers.
If you set this variable to
nilin a buffer, that buffer does not have a mode line. (A window that is just one line tall never displays a mode line.)
The default value of mode-line-format is designed to use the
values of other variables such as mode-line-position and
mode-line-modes (which in turn incorporates the values of the
variables mode-name and minor-mode-alist). Very few
modes need to alter mode-line-format itself. For most
purposes, it is sufficient to alter some of the variables that
mode-line-format either directly or indirectly refers to.
If you do alter mode-line-format itself, the new value should
use the same variables that appear in the default value (see Mode Line Variables), rather than duplicating their contents or displaying
the information in another fashion. This way, customizations made by
the user or by Lisp programs (such as display-time and major
modes) via changes to those variables remain effective.
Here is an example of a mode-line-format that might be
useful for shell-mode, since it contains the host name and default
directory.
(setq mode-line-format
(list "-"
'mode-line-mule-info
'mode-line-modified
'mode-line-frame-identification
"%b--"
;; Note that this is evaluated while making the list.
;; It makes a mode-line construct which is just a string.
(getenv "HOST")
":"
'default-directory
" "
'global-mode-string
" %[("
'(:eval (mode-line-mode-name))
'mode-line-process
'minor-mode-alist
"%n"
")%]--"
'(which-func-mode ("" which-func-format "--"))
'(line-number-mode "L%l--")
'(column-number-mode "C%c--")
'(-3 "%p")
"-%-"))
(The variables line-number-mode, column-number-mode
and which-func-mode enable particular minor modes; as usual,
these variable names are also the minor mode command names.)
This section describes variables incorporated by the standard value
of mode-line-format into the text of the mode line. There is
nothing inherently special about these variables; any other variables
could have the same effects on the mode line if
mode-line-format's value were changed to use them. However,
various parts of Emacs set these variables on the understanding that
they will control parts of the mode line; therefore, practically
speaking, it is essential for the mode line to use them.
This variable holds the value of the mode-line construct that displays information about the language environment, buffer coding system, and current input method. See Non-ASCII Characters.
This variable holds the value of the mode-line construct that displays whether the current buffer is modified. Its default value displays ‘**’ if the buffer is modified, ‘--’ if the buffer is not modified, ‘%%’ if the buffer is read only, and ‘%*’ if the buffer is read only and modified.
Changing this variable does not force an update of the mode line.
This variable identifies the current frame. Its default value displays
" "if you are using a window system which can show multiple frames, or"-%F "on an ordinary terminal which shows only one frame at a time.
This variable identifies the buffer being displayed in the window. Its default value displays the buffer name, padded with spaces to at least 12 columns.
This variable indicates the position in the buffer. Its default value displays the buffer percentage and, optionally, the buffer size, the line number and the column number.
The variable
vc-mode, buffer-local in each buffer, records whether the buffer's visited file is maintained with version control, and, if so, which kind. Its value is a string that appears in the mode line, ornilfor no version control.
This variable displays the buffer's major and minor modes. Its default value also displays the recursive editing level, information on the process status, and whether narrowing is in effect.
The following three variables are used in mode-line-modes:
This buffer-local variable holds the “pretty” name of the current buffer's major mode. Each major mode should set this variable so that the mode name will appear in the mode line. The value does not have to be a string, but can use any of the data types valid in a mode-line construct (see Mode Line Data). To compute the string that will identify the mode name in the mode line, use
format-mode-line(see Emulating Mode Line).
This buffer-local variable contains the mode-line information on process status in modes used for communicating with subprocesses. It is displayed immediately following the major mode name, with no intervening space. For example, its value in the ‘*shell*’ buffer is
(":%s"), which allows the shell to display its status along with the major mode as: ‘(Shell:run)’. Normally this variable isnil.
This variable holds an association list whose elements specify how the mode line should indicate that a minor mode is active. Each element of the
minor-mode-alistshould be a two-element list:(minor-mode-variable mode-line-string)More generally, mode-line-string can be any mode-line spec. It appears in the mode line when the value of minor-mode-variable is non-
nil, and not otherwise. These strings should begin with spaces so that they don't run together. Conventionally, the minor-mode-variable for a specific mode is set to a non-nilvalue when that minor mode is activated.
minor-mode-alistitself is not buffer-local. Each variable mentioned in the alist should be buffer-local if its minor mode can be enabled separately in each buffer.
This variable holds a mode-line spec that, by default, appears in the mode line just after the
which-func-modeminor mode if set, else aftermode-line-modes. The commanddisplay-timesetsglobal-mode-stringto refer to the variabledisplay-time-string, which holds a string containing the time and load information.The ‘%M’ construct substitutes the value of
global-mode-string, but that is obsolete, since the variable is included in the mode line frommode-line-format.
Here is a simplified version of the default value of
mode-line-format. The real default value also
specifies addition of text properties.
("-"
mode-line-mule-info
mode-line-modified
mode-line-frame-identification
mode-line-buffer-identification
" "
mode-line-position
(vc-mode vc-mode)
" "
mode-line-modes
(which-func-mode ("" which-func-format "--"))
(global-mode-string ("--" global-mode-string))
"-%-")
%-Constructs in the Mode LineStrings used as mode-line constructs can use certain
%-constructs to substitute various kinds of data. Here is a
list of the defined %-constructs, and what they mean. In any
construct except ‘%%’, you can add a decimal integer after the
‘%’ to specify a minimum field width. If the width is less, the
field is padded with spaces to the right.
%bbuffer-name function.
See Buffer Names.
%c%e%fbuffer-file-name
function. See Buffer File Name.
%F%i(- (point-max) (point-min)).
%I%l%nnarrow-to-region in Narrowing).
%p%P%sprocess-status. See Process Information.
%t%z%Z%*buffer-read-only); buffer-modified-p); %+buffer-modified-p); buffer-read-only); %&%[%]%-%%%-constructs are allowed.
The following two %-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
mode-name and global-mode-string.
%mmode-name.
%Mglobal-mode-string.
Certain text properties are meaningful in the
mode line. The face property affects the appearance of text; the
help-echo property associates help strings with the text, and
local-map can make the text mouse-sensitive.
There are four ways to specify text properties for text in the mode line:
(:propertize elt props...) construct to
give elt a text property specified by props.
:eval form in the mode-line data
structure, and make form evaluate to a string that has a text
property.
You can use the local-map property to specify a keymap. This
keymap only takes real effect for mouse clicks; binding character keys
and function keys to it has no effect, since it is impossible to move
point into the mode line.
When the mode line refers to a variable which does not have a
non-nil risky-local-variable property, any text
properties given or specified within that variable's values are
ignored. This is because such properties could otherwise specify
functions to be called, and those functions could come from file
local variables.
A window can have a header line at the top, just as it can have a mode line at the bottom. The header line feature works just like the mode-line feature, except that it's controlled by different variables.
This variable, local in every buffer, specifies how to display the header line, for windows displaying the buffer. The format of the value is the same as for
mode-line-format(see Mode Line Data). It is normallynil, so that ordinary buffers have no header line.
A window that is just one line tall never displays a header line. A window that is two lines tall cannot display both a mode line and a header line at once; if it has a mode line, then it does not display a header line.
You can use the function format-mode-line to compute
the text that would appear in a mode line or header line
based on a certain mode-line specification.
This function formats a line of text according to format as if it were generating the mode line for window, but it also returns the text as a string. The argument window defaults to the selected window. If buffer is non-
nil, all the information used is taken from buffer; by default, it comes from window's buffer.The value string normally has text properties that correspond to the faces, keymaps, etc., that the mode line would have. Any character for which no
faceproperty is specified by format gets a default value determined by face. If face ist, that stands for eithermode-lineif window is selected, otherwisemode-line-inactive. If face isnilor omitted, that stands for the default face. If face is an integer, the value returned by this function will have no text properties.You can also specify other valid faces as the value of face. If specified, that face provides the
faceproperty for characters whose face is not specified by format.Note that using
mode-line,mode-line-inactive, orheader-lineas face will actually redisplay the mode line or the header line, respectively, using the current definitions of the corresponding face, in addition to returning the formatted string. (Other faces do not cause redisplay.)For example,
(format-mode-line header-line-format)returns the text that would appear in the selected window's header line (""if it has no header line).(format-mode-line header-line-format 'header-line)returns the same text, with each character carrying the face that it will have in the header line itself, and also redraws the header line.
Imenu is a feature that lets users select a definition or
section in the buffer, from a menu which lists all of them, to go
directly to that location in the buffer. Imenu works by constructing
a buffer index which lists the names and buffer positions of the
definitions, or other named portions of the buffer; then the user can
choose one of them and move point to it. Major modes can add a menu
bar item to use Imenu using imenu-add-to-menubar.
This function defines a local menu bar item named name to run Imenu.
The user-level commands for using Imenu are described in the Emacs Manual (see Imenu). This section explains how to customize Imenu's method of finding definitions or buffer portions for a particular major mode.
The usual and simplest way is to set the variable
imenu-generic-expression:
This variable, if non-
nil, is a list that specifies regular expressions for finding definitions for Imenu. Simple elements ofimenu-generic-expressionlook like this:(menu-title regexp index)Here, if menu-title is non-
nil, it says that the matches for this element should go in a submenu of the buffer index; menu-title itself specifies the name for the submenu. If menu-title isnil, the matches for this element go directly in the top level of the buffer index.The second item in the list, regexp, is a regular expression (see Regular Expressions); anything in the buffer that it matches is considered a definition, something to mention in the buffer index. The third item, index, is a non-negative integer that indicates which subexpression in regexp matches the definition's name.
An element can also look like this:
(menu-title regexp index function arguments...)Each match for this element creates an index item, and when the index item is selected by the user, it calls function with arguments consisting of the item name, the buffer position, and arguments.
For Emacs Lisp mode,
imenu-generic-expressioncould look like this:((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Types*" "^\\s-*\ (def\\(type\\|struct\\|class\\|ine-condition\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2))Setting this variable makes it buffer-local in the current buffer.
This variable controls whether matching against the regular expressions in the value of
imenu-generic-expressionis case-sensitive:t, the default, means matching should ignore case.Setting this variable makes it buffer-local in the current buffer.
This variable is an alist of syntax table modifiers to use while processing
imenu-generic-expression, to override the syntax table of the current buffer. Each element should have this form:(characters . syntax-description)The car, characters, can be either a character or a string. The element says to give that character or characters the syntax specified by syntax-description, which is passed to
modify-syntax-entry(see Syntax Table Functions).This feature is typically used to give word syntax to characters which normally have symbol syntax, and thus to simplify
imenu-generic-expressionand speed up matching. For example, Fortran mode uses it this way:(setq imenu-syntax-alist '(("_$" . "w")))The
imenu-generic-expressionregular expressions can then use ‘\\sw+’ instead of ‘\\(\\sw\\|\\s_\\)+’. Note that this technique may be inconvenient when the mode needs to limit the initial character of a name to a smaller set of characters than are allowed in the rest of a name.Setting this variable makes it buffer-local in the current buffer.
Another way to customize Imenu for a major mode is to set the
variables imenu-prev-index-position-function and
imenu-extract-index-name-function:
If this variable is non-
nil, its value should be a function that finds the next “definition” to put in the buffer index, scanning backward in the buffer from point. It should returnnilif it doesn't find another “definition” before point. Otherwise it should leave point at the place it finds a “definition” and return any non-nilvalue.Setting this variable makes it buffer-local in the current buffer.
If this variable is non-
nil, its value should be a function to return the name for a definition, assuming point is in that definition as theimenu-prev-index-position-functionfunction would leave it.Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the
variable imenu-create-index-function:
This variable specifies the function to use for creating a buffer index. The function should take no arguments, and return an index alist for the current buffer. It is called within
save-excursion, so where it leaves point makes no difference.The index alist can have three types of elements. Simple elements look like this:
(index-name . index-position)Selecting a simple element has the effect of moving to position index-position in the buffer. Special elements look like this:
(index-name index-position function arguments...)Selecting a special element performs:
(funcall function index-name index-position arguments...)A nested sub-alist element looks like this:
(menu-title sub-alist)It creates the submenu menu-title specified by sub-alist.
The default value of
imenu-create-index-functionisimenu-default-create-index-function. This function calls the value ofimenu-prev-index-position-functionand the value ofimenu-extract-index-name-functionto produce the index alist. However, if either of these two variables isnil, the default function usesimenu-generic-expressioninstead.Setting this variable makes it buffer-local in the current buffer.
Font Lock mode is a feature that automatically attaches
face properties to certain parts of the buffer based on their
syntactic role. How it parses the buffer depends on the major mode;
most major modes define syntactic criteria for which faces to use in
which contexts. This section explains how to customize Font Lock for a
particular major mode.
Font Lock mode finds text to highlight in two ways: through syntactic parsing based on the syntax table, and through searching (usually for regular expressions). Syntactic fontification happens first; it finds comments and string constants and highlights them. Search-based fontification happens second.
There are several variables that control how Font Lock mode highlights
text. But major modes should not set any of these variables directly.
Instead, they should set font-lock-defaults as a buffer-local
variable. The value assigned to this variable is used, if and when Font
Lock mode is enabled, to set all the other variables.
This variable is set by major modes, as a buffer-local variable, to specify how to fontify text in that mode. It automatically becomes buffer-local when you set it. If its value is
nil, Font-Lock mode does no highlighting, and you can use the ‘Faces’ menu (under ‘Edit’ and then ‘Text Properties’ in the menu bar) to assign faces explicitly to text in the buffer.If non-
nil, the value should look like this:(keywords [keywords-only [case-fold [syntax-alist [syntax-begin other-vars...]]]])The first element, keywords, indirectly specifies the value of
font-lock-keywordswhich directs search-based fontification. It can be a symbol, a variable or a function whose value is the list to use forfont-lock-keywords. It can also be a list of several such symbols, one for each possible level of fontification. The first symbol specifies the ‘mode default’ level of fontification, the next symbol level 1 fontification, the next level 2, and so on. The ‘mode default’ level is normally the same as level 1. It is used whenfont-lock-maximum-decorationhas anilvalue. See Levels of Font Lock.The second element, keywords-only, specifies the value of the variable
font-lock-keywords-only. If this is omitted ornil, syntactic fontification (of strings and comments) is also performed. If this is non-nil, such fontification is not performed. See Syntactic Font Lock.The third element, case-fold, specifies the value of
font-lock-keywords-case-fold-search. If it is non-nil, Font Lock mode ignores case when searching as directed byfont-lock-keywords.If the fourth element, syntax-alist, is non-
nil, it should be a list of cons cells of the form(char-or-string.string). These are used to set up a syntax table for syntactic fontification (see Syntax Table Functions). The resulting syntax table is stored infont-lock-syntax-table.The fifth element, syntax-begin, specifies the value of
font-lock-beginning-of-syntax-function. We recommend setting this variable toniland usingsyntax-begin-functioninstead.All the remaining elements (if any) are collectively called other-vars. Each of these elements should have the form
(variable.value)—which means, make variable buffer-local and then set it to value. You can use these other-vars to set other variables that affect fontification, aside from those you can control with the first five elements. See Other Font Lock Variables.
If your mode fontifies text explicitly by adding
font-lock-face properties, it can specify (nil t) for
font-lock-defaults to turn off all automatic fontification.
However, this is not required; it is possible to fontify some things
using font-lock-face properties and set up automatic
fontification for other parts of the text.
The most important variable for customizing Font Lock mode is
font-lock-keywords. It specifies the search criteria for
search-based fontification. You should specify the value of this
variable with keywords in font-lock-defaults.
This variable's value is a list of the keywords to highlight. Be careful when composing regular expressions for this list; a poorly written pattern can dramatically slow things down!
Each element of font-lock-keywords specifies how to find
certain cases of text, and how to highlight those cases. Font Lock mode
processes the elements of font-lock-keywords one by one, and for
each element, it finds and handles all matches. Ordinarily, once
part of the text has been fontified already, this cannot be overridden
by a subsequent match in the same text; but you can specify different
behavior using the override element of a subexp-highlighter.
Each element of font-lock-keywords should have one of these
forms:
font-lock-keyword-face. For example,
;; Highlight occurrences of the word ‘foo’
;; using font-lock-keyword-face.
"\\<foo\\>"
The function regexp-opt (see Regexp Functions) is useful
for calculating optimal regular expressions to match a number of
different keywords.
font-lock-keyword-face.
When function is called, it receives one argument, the limit of
the search; it should begin searching at point, and not search beyond the
limit. It should return non-nil if it succeeds, and set the
match data to describe the match that was found. Returning nil
indicates failure of the search.
Fontification will call function repeatedly with the same limit,
and with point where the previous invocation left it, until
function fails. On failure, function need not reset point
in any particular way.
(matcher . subexp) ;; Highlight the ‘bar’ in each occurrence of ‘fubar’,
;; using font-lock-keyword-face.
("fu\\(bar\\)" . 1)
If you use regexp-opt to produce the regular expression
matcher, you can use regexp-opt-depth (see Regexp Functions) to calculate the value for subexp.
(matcher . facespec) ;; Highlight occurrences of ‘fubar’,
;; using the face which is the value of fubar-face.
("fubar" . fubar-face)
However, facespec can also evaluate to a list of this form:
(face face prop1 val1 prop2 val2...)
to specify the face face and various additional text properties
to put on the text that matches. If you do this, be sure to add the
other text property names that you set in this way to the value of
font-lock-extra-managed-props so that the properties will also
be cleared out when they are no longer appropriate. Alternatively,
you can set the variable font-lock-unfontify-region-function to
a function that clears these properties. See Other Font Lock Variables.
(matcher . subexp-highlighter)(subexp facespec [override [laxmatch]])
The car, subexp, is an integer specifying which subexpression of the match to fontify (0 means the entire matching text). The second subelement, facespec, is an expression whose value specifies the face, as described above.
The last two values in subexp-highlighter, override and
laxmatch, are optional flags. If override is t,
this element can override existing fontification made by previous
elements of font-lock-keywords. If it is keep, then
each character is fontified if it has not been fontified already by
some other element. If it is prepend, the face specified by
facespec is added to the beginning of the font-lock-face
property. If it is append, the face is added to the end of the
font-lock-face property.
If laxmatch is non-nil, it means there should be no error
if there is no subexpression numbered subexp in matcher.
Obviously, fontification of the subexpression numbered subexp will
not occur. However, fontification of other subexpressions (and other
regexps) will continue. If laxmatch is nil, and the
specified subexpression is missing, then an error is signaled which
terminates search-based fontification.
Here are some examples of elements of this kind, and what they do:
;; Highlight occurrences of either ‘foo’ or ‘bar’, using ;;foo-bar-face, even if they have already been highlighted. ;;foo-bar-faceshould be a variable whose value is a face. ("foo\\|bar" 0 foo-bar-face t) ;; Highlight the first subexpression within each occurrence ;; that the functionfubar-matchfinds, ;; using the face which is the value offubar-face. (fubar-match 1 fubar-face)
(matcher . anchored-highlighter) (anchored-matcher pre-form post-form
subexp-highlighters...)
Here, anchored-matcher, like matcher, is either a regular expression or a function. After a match of matcher is found, point is at the end of the match. Now, Font Lock evaluates the form pre-form. Then it searches for matches of anchored-matcher and uses subexp-highlighters to highlight these. A subexp-highlighter is as described above. Finally, Font Lock evaluates post-form.
The forms pre-form and post-form can be used to initialize before, and cleanup after, anchored-matcher is used. Typically, pre-form is used to move point to some position relative to the match of matcher, before starting with anchored-matcher. post-form might be used to move back, before resuming with matcher.
After Font Lock evaluates pre-form, it does not search for anchored-matcher beyond the end of the line. However, if pre-form returns a buffer position that is greater than the position of point after pre-form is evaluated, then the position returned by pre-form is used as the limit of the search instead. It is generally a bad idea to return a position greater than the end of the line; in other words, the anchored-matcher search should not span lines.
For example,
;; Highlight occurrences of the word ‘item’ following
;; an occurrence of the word ‘anchor’ (on the same line)
;; in the value of item-face.
("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face))
Here, pre-form and post-form are nil. Therefore
searching for ‘item’ starts at the end of the match of
‘anchor’, and searching for subsequent instances of ‘anchor’
resumes from where searching for ‘item’ concluded.
(matcher highlighters...)For example,
;; Highlight occurrences of the word ‘anchor’ in the value ;; ofanchor-face, and subsequent occurrences of the word ;; ‘item’ (on the same line) in the value ofitem-face. ("\\<anchor\\>" (0 anchor-face) ("\\<item\\>" nil nil (0 item-face)))
(eval . form)font-lock-keywords is used in a buffer.
Its value should have one of the forms described in this table.
Warning: Do not design an element of font-lock-keywords
to match text which spans lines; this does not work reliably.
For details, see See Multiline Font Lock.
You can use case-fold in font-lock-defaults to specify
the value of font-lock-keywords-case-fold-search which says
whether search-based fontification should be case-insensitive.
Non-
nilmeans that regular expression matching for the sake offont-lock-keywordsshould be case-insensitive.
You can use font-lock-add-keywords to add additional
search-based fontification rules to a major mode, and
font-lock-remove-keywords to remove rules.
This function adds highlighting keywords, for the current buffer or for major mode mode. The argument keywords should be a list with the same format as the variable
font-lock-keywords.If mode is a symbol which is a major mode command name, such as
c-mode, the effect is that enabling Font Lock mode in mode will add keywords tofont-lock-keywords. Calling with a non-nilvalue of mode is correct only in your ~/.emacs file.If mode is
nil, this function adds keywords tofont-lock-keywordsin the current buffer. This way of callingfont-lock-add-keywordsis usually used in mode hook functions.By default, keywords are added at the beginning of
font-lock-keywords. If the optional argument how isset, they are used to replace the value offont-lock-keywords. If how is any other non-nilvalue, they are added at the end offont-lock-keywords.Some modes provide specialized support you can use in additional highlighting patterns. See the variables
c-font-lock-extra-types,c++-font-lock-extra-types, andjava-font-lock-extra-types, for example.Warning: major mode functions must not call
font-lock-add-keywordsunder any circumstances, either directly or indirectly, except through their mode hooks. (Doing so would lead to incorrect behavior for some minor modes.) They should set up their rules for search-based fontification by settingfont-lock-keywords.
This function removes keywords from
font-lock-keywordsfor the current buffer or for major mode mode. As infont-lock-add-keywords, mode should be a major mode command name ornil. All the caveats and requirements forfont-lock-add-keywordsapply here too.
For example, this code
(font-lock-add-keywords 'c-mode
'(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face)))
adds two fontification patterns for C mode: one to fontify the word ‘FIXME’, even in comments, and another to fontify the words ‘and’, ‘or’ and ‘not’ as keywords.
That example affects only C mode proper. To add the same patterns to C mode and all modes derived from it, do this instead:
(add-hook 'c-mode-hook
(lambda ()
(font-lock-add-keywords nil
'(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
("\\<\\(and\\|or\\|not\\)\\>" .
font-lock-keyword-face)))))
This section describes additional variables that a major mode can
set by means of other-vars in font-lock-defaults
(see Font Lock Basics).
If this variable is non-
nil, it should be a function that is called with no arguments, to choose an enclosing range of text for refontification for the command M-o M-o (font-lock-fontify-block).The function should report its choice by placing the region around it. A good choice is a range of text large enough to give proper results, but not too large so that refontification becomes slow. Typical values are
mark-defunfor programming modes ormark-paragraphfor textual modes.
This variable specifies additional properties (other than
font-lock-face) that are being managed by Font Lock mode. It is used byfont-lock-default-unfontify-region, which normally only manages thefont-lock-faceproperty. If you want Font Lock to manage other properties as well, you must specify them in a facespec infont-lock-keywordsas well as add them to this list. See Search-based Fontification.
Function to use for fontifying the buffer. The default value is
font-lock-default-fontify-buffer.
Function to use for unfontifying the buffer. This is used when turning off Font Lock mode. The default value is
font-lock-default-unfontify-buffer.
Function to use for fontifying a region. It should take two arguments, the beginning and end of the region, and an optional third argument verbose. If verbose is non-
nil, the function should print status messages. The default value isfont-lock-default-fontify-region.
Function to use for unfontifying a region. It should take two arguments, the beginning and end of the region. The default value is
font-lock-default-unfontify-region.
This function tells Font Lock mode to run the Lisp function function any time it has to fontify or refontify part of the current buffer. It calls function before calling the default fontification functions, and gives it two arguments, start and end, which specify the region to be fontified or refontified.
The optional argument contextual, if non-
nil, forces Font Lock mode to always refontify a syntactically relevant part of the buffer, and not just the modified lines. This argument can usually be omitted.
If function was previously registered as a fontification function using
jit-lock-register, this function unregisters it.
Many major modes offer three different levels of fontification. You
can define multiple levels by using a list of symbols for keywords
in font-lock-defaults. Each symbol specifies one level of
fontification; it is up to the user to choose one of these levels,
normally by setting font-lock-maximum-decoration (see Font Lock). The chosen level's symbol
value is used to initialize font-lock-keywords.
Here are the conventions for how to define the levels of fontification:
Some major modes such as list-buffers and occur
construct the buffer text programmatically. The easiest way for them
to support Font Lock mode is to specify the faces of text when they
insert the text in the buffer.
The way to do this is to specify the faces in the text with the
special text property font-lock-face (see Special Properties). When Font Lock mode is enabled, this property controls
the display, just like the face property. When Font Lock mode
is disabled, font-lock-face has no effect on the display.
It is ok for a mode to use font-lock-face for some text and
also use the normal Font Lock machinery. But if the mode does not use
the normal Font Lock machinery, it should not set the variable
font-lock-defaults.
You can make Font Lock mode use any face, but several faces are
defined specifically for Font Lock mode. Each of these symbols is both
a face name, and a variable whose default value is the symbol itself.
Thus, the default value of font-lock-comment-face is
font-lock-comment-face. This means you can write
font-lock-comment-face in a context such as
font-lock-keywords where a face-name-valued expression is used.
font-lock-comment-facefont-lock-comment-delimiter-facefont-lock-doc-facefont-lock-string-facefont-lock-keyword-facefor and if in C.
font-lock-builtin-facefont-lock-function-name-facefont-lock-variable-name-facefont-lock-type-facefont-lock-constant-facefont-lock-preprocessor-facefont-lock-negation-char-facefont-lock-warning-face#error
directives in C.
Syntactic fontification uses the syntax table to find comments and
string constants (see Syntax Tables). It highlights them using
font-lock-comment-face and font-lock-string-face
(see Faces for Font Lock), or whatever
font-lock-syntactic-face-function chooses. There are several
variables that affect syntactic fontification; you should set them by
means of font-lock-defaults (see Font Lock Basics).
Non-
nilmeans Font Lock should not do syntactic fontification; it should only fontify based onfont-lock-keywords. The normal way for a mode to set this variable totis with keywords-only infont-lock-defaults.
This variable holds the syntax table to use for fontification of comments and strings. Specify it using syntax-alist in
font-lock-defaults. If this isnil, fontification uses the buffer's syntax table.
If this variable is non-
nil, it should be a function to move point back to a position that is syntactically at “top level” and outside of strings or comments. Font Lock uses this when necessary to get the right results for syntactic fontification.This function is called with no arguments. It should leave point at the beginning of any enclosing syntactic block. Typical values are
beginning-of-line(used when the start of the line is known to be outside a syntactic block), orbeginning-of-defunfor programming modes, orbackward-paragraphfor textual modes.If the value is
nil, Font Lock usessyntax-begin-functionto move back outside of any comment, string, or sexp. This variable is semi-obsolete; we recommend settingsyntax-begin-functioninstead.Specify this variable using syntax-begin in
font-lock-defaults.
A function to determine which face to use for a given syntactic element (a string or a comment). The function is called with one argument, the parse state at point returned by
parse-partial-sexp, and should return a face. The default value returnsfont-lock-comment-facefor comments andfont-lock-string-facefor strings.This can be used to highlighting different kinds of strings or comments differently. It is also sometimes abused together with
font-lock-syntactic-keywordsto highlight constructs that span multiple lines, but this is too esoteric to document here.Specify this variable using other-vars in
font-lock-defaults.
Font Lock mode can be used to update syntax-table properties
automatically (see Syntax Properties). This is useful in
languages for which a single syntax table by itself is not sufficient.
This variable enables and controls updating
syntax-tableproperties by Font Lock. Its value should be a list of elements of this form:(matcher subexp syntax override laxmatch)The parts of this element have the same meanings as in the corresponding sort of element of
font-lock-keywords,(matcher subexp facespec override laxmatch)However, instead of specifying the value facespec to use for the
faceproperty, it specifies the value syntax to use for thesyntax-tableproperty. Here, syntax can be a string (as taken bymodify-syntax-entry), a syntax table, a cons cell (as returned bystring-to-syntax), or an expression whose value is one of those two types. override cannot beprependorappend.For example, an element of the form:
("\\$\\(#\\)" 1 ".")highlights syntactically a hash character when following a dollar character, with a SYNTAX of
"."(meaning punctuation syntax). Assuming that the buffer syntax table specifies hash characters to have comment start syntax, the element will only highlight hash characters that do not follow dollar characters as comments syntactically.An element of the form:
("\\('\\).\\('\\)" (1 "\"") (2 "\""))highlights syntactically both single quotes which surround a single character, with a SYNTAX of
"\""(meaning string quote syntax). Assuming that the buffer syntax table does not specify single quotes to have quote syntax, the element will only highlight single quotes of the form ‘'c'’ as strings syntactically. Other forms, such as ‘foo'bar’ or ‘'fubar'’, will not be highlighted as strings.Major modes normally set this variable with other-vars in
font-lock-defaults.
Normally, elements of font-lock-keywords should not match
across multiple lines; that doesn't work reliably, because Font Lock
usually scans just part of the buffer, and it can miss a multi-line
construct that crosses the line boundary where the scan starts. (The
scan normally starts at the beginning of a line.)
Making elements that match multiline constructs work properly has two aspects: correct identification and correct rehighlighting. The first means that Font Lock finds all multiline constructs. The second means that Font Lock will correctly rehighlight all the relevant text when a multiline construct is changed—for example, if some of the text that was previously part of a multiline construct ceases to be part of it. The two aspects are closely related, and often getting one of them to work will appear to make the other also work. However, for reliable results you must attend explicitly to both aspects.
There are three ways to ensure correct identification of multiline constructs:
font-lock-extend-region-functions that does
the identification and extends the scan so that the scanned
text never starts or ends in the middle of a multiline construct.
font-lock-fontify-region-function hook similarly to
extend the scan so that the scanned text never starts or ends in the
middle of a multiline construct.
font-lock-multiline
which will instruct font-lock not to start or end the scan in the
middle of the construct.
There are three ways to do rehighlighting of multiline constructs:
font-lock-multiline property on the construct. This
will rehighlight the whole construct if any part of it is changed. In
some cases you can do this automatically by setting the
font-lock-multiline variable, which see.
jit-lock-contextually is set and rely on it doing its
job. This will only rehighlight the part of the construct that
follows the actual change, and will do it after a short delay.
This only works if the highlighting of the various parts of your
multiline construct never depends on text in subsequent lines.
Since jit-lock-contextually is activated by default, this can
be an attractive solution.
jit-lock-defer-multiline property on the construct.
This works only if jit-lock-contextually is used, and with the
same delay before rehighlighting, but like font-lock-multiline,
it also handles the case where highlighting depends on
subsequent lines.
One way to ensure reliable rehighlighting of multiline Font Lock
constructs is to put on them the text property font-lock-multiline.
It should be present and non-nil for text that is part of a
multiline construct.
When Font Lock is about to highlight a range of text, it first
extends the boundaries of the range as necessary so that they do not
fall within text marked with the font-lock-multiline property.
Then it removes any font-lock-multiline properties from the
range, and highlights it. The highlighting specification (mostly
font-lock-keywords) must reinstall this property each time,
whenever it is appropriate.
Warning: don't use the font-lock-multiline property
on large ranges of text, because that will make rehighlighting slow.
If the
font-lock-multilinevariable is set tot, Font Lock will try to add thefont-lock-multilineproperty automatically on multiline constructs. This is not a universal solution, however, since it slows down Font Lock somewhat. It can miss some multiline constructs, or make the property larger or smaller than necessary.For elements whose matcher is a function, the function should ensure that submatch 0 covers the whole relevant multiline construct, even if only a small subpart will be highlighted. It is often just as easy to add the
font-lock-multilineproperty by hand.
The font-lock-multiline property is meant to ensure proper
refontification; it does not automatically identify new multiline
constructs. Identifying the requires that Font-Lock operate on large
enough chunks at a time. This will happen by accident on many cases,
which may give the impression that multiline constructs magically work.
If you set the font-lock-multiline variable non-nil,
this impression will be even stronger, since the highlighting of those
constructs which are found will be properly updated from then on.
But that does not work reliably.
To find multiline constructs reliably, you must either manually
place the font-lock-multiline property on the text before
Font-Lock looks at it, or use
font-lock-fontify-region-function.
When a buffer is changed, the region that Font Lock refontifies is by default the smallest sequence of whole lines that spans the change. While this works well most of the time, sometimes it doesn't—for example, when a change alters the syntactic meaning of text on an earlier line.
You can enlarge (or even reduce) the region to fontify by setting one the following variables:
This buffer-local variable is either
nilor a function for Font-Lock to call to determine the region to scan and fontify.The function is given three parameters, the standard beg, end, and old-len from after-change-functions (see Change Hooks). It should return either a cons of the beginning and end buffer positions (in that order) of the region to fontify, or
nil(which means choose the region in the standard way). This function needs to preserve point, the match-data, and the current restriction. The region it returns may start or end in the middle of a line.Since this function is called after every buffer change, it should be reasonably fast.
For programming languages, an important feature of a major mode is to
provide automatic indentation. This is controlled in Emacs by
indent-line-function (see Mode-Specific Indent).
Writing a good indentation function can be difficult and to a large
extent it is still a black art.
Many major mode authors will start by writing a simple indentation function that works for simple cases, for example by comparing with the indentation of the previous text line. For most programming languages that are not really line-based, this tends to scale very poorly: improving such a function to let it handle more diverse situations tends to become more and more difficult, resulting in the end with a large, complex, unmaintainable indentation function which nobody dares to touch.
A good indentation function will usually need to actually parse the text, according to the syntax of the language. Luckily, it is not necessary to parse the text in as much detail as would be needed for a compiler, but on the other hand, the parser embedded in the indentation code will want to be somewhat friendly to syntactically incorrect code.
Good maintainable indentation functions usually fall into 2 categories: either parsing forward from some “safe” starting point until the position of interest, or parsing backward from the position of interest. Neither of the two is a clearly better choice than the other: parsing backward is often more difficult than parsing forward because programming languages are designed to be parsed forward, but for the purpose of indentation it has the advantage of not needing to guess a “safe” starting point, and it generally enjoys the property that only a minimum of text will be analyzed to decide the indentation of a line, so indentation will tend to be unaffected by syntax errors in some earlier unrelated piece of code. Parsing forward on the other hand is usually easier and has the advantage of making it possible to reindent efficiently a whole region at a time, with a single parse.
Rather than write your own indentation function from scratch, it is often preferable to try and reuse some existing ones or to rely on a generic indentation engine. There are sadly few such engines. The CC-mode indentation code (used with C, C++, Java, Awk and a few other such modes) has been made more generic over the years, so if your language seems somewhat similar to one of those languages, you might try to use that engine. Another one is SMIE which takes an approach in the spirit of Lisp sexps and adapts it to non-Lisp languages.
SMIE is a package that provides a generic navigation and indentation engine. Based on a very simple parser using an “operator precedence grammar”, it lets major modes extend the sexp-based navigation of Lisp to non-Lisp languages as well as provide a simple to use but reliable auto-indentation.
Operator precedence grammar is a very primitive technology for parsing
compared to some of the more common techniques used in compilers.
It has the following characteristics: its parsing power is very limited,
and it is largely unable to detect syntax errors, but it has the
advantage of being algorithmically efficient and able to parse forward
just as well as backward. In practice that means that SMIE can use it
for indentation based on backward parsing, that it can provide both
forward-sexp and backward-sexp functionality, and that it
will naturally work on syntactically incorrect code without any extra
effort. The downside is that it also means that most programming
languages cannot be parsed correctly using SMIE, at least not without
resorting to some special tricks (see SMIE Tricks).
SMIE is meant to be a one-stop shop for structural navigation and
various other features which rely on the syntactic structure of code, in
particular automatic indentation. The main entry point is
smie-setup which is a function typically called while setting
up a major mode.
Setup SMIE navigation and indentation. grammar is a grammar table generated by
smie-prec2->grammar. rules-function is a set of indentation rules for use onsmie-rules-function. keywords are additional arguments, which can include the following keywords:
:forward-tokenfun: Specify the forward lexer to use.:backward-tokenfun: Specify the backward lexer to use.
Calling this function is sufficient to make commands such as
forward-sexp, backward-sexp, and transpose-sexps be
able to properly handle structural elements other than just the paired
parentheses already handled by syntax tables. For example, if the
provided grammar is precise enough, transpose-sexps can correctly
transpose the two arguments of a + operator, taking into account
the precedence rules of the language.
Calling `smie-setup' is also sufficient to make TAB indentation work in the expected way, and provides some commands that you can bind in the major mode keymap.
This command closes the most recently opened (and not yet closed) block.
This command is like
down-listbut it also pays attention to nesting of tokens other than parentheses, such asbegin...end.
SMIE's precedence grammars simply give to each token a pair of
precedences: the left-precedence and the right-precedence. We say
T1 < T2 if the right-precedence of token T1 is less than
the left-precedence of token T2. A good way to read this
< is as a kind of parenthesis: if we find ... T1 something
T2 ... then that should be parsed as ... T1 (something T2 ...
rather than as ... T1 something) T2 .... The latter
interpretation would be the case if we had T1 > T2. If we have
T1 = T2, it means that token T2 follows token T1 in the same
syntactic construction, so typically we have "begin" = "end".
Such pairs of precedences are sufficient to express left-associativity
or right-associativity of infix operators, nesting of tokens like
parentheses and many other cases.
This function takes a prec2 grammar table and returns an alist suitable for use in
smie-setup. The prec2 table is itself meant to be built by one of the functions below.
This function takes several prec2 tables and merges them into a new prec2 table.
This function builds a prec2 table from a table of precedences precs. precs should be a list, sorted by precedence (for example
"+"will come before"*"), of elements of the form(assoc op...), where each op is a token that acts as an operator; assoc is their associativity, which can be eitherleft,right,assoc, ornonassoc. All operators in a given element share the same precedence level and associativity.
This function lets you specify the grammar using a BNF notation. It accepts a bnf description of the grammar along with a set of conflict resolution rules resolvers, and returns a prec2 table.
bnf is a list of nonterminal definitions of the form
(nonterm rhs1 rhs2...)where each rhs is a (non-empty) list of terminals (aka tokens) or non-terminals.Not all grammars are accepted:
- An rhs cannot be an empty list (an empty list is never needed, since SMIE allows all non-terminals to match the empty string anyway).
- An rhs cannot have 2 consecutive non-terminals: each pair of non-terminals needs to be separated by a terminal (aka token). This is a fundamental limitation of operator precedence grammars.
Additionally, conflicts can occur:
- The returned prec2 table holds constraints between pairs of tokens, and for any given pair only one constraint can be present: T1 < T2, T1 = T2, or T1 > T2.
- A token can be an
opener(something similar to an open-paren), acloser(like a close-paren), orneitherof the two (e.g. an infix operator, or an inner token like"else").Precedence conflicts can be resolved via resolvers, which is a list of precs tables (see
smie-precs->prec2): for each precedence conflict, if thoseprecstables specify a particular constraint, then the conflict is resolved by using this constraint instead, else a conflict is reported and one of the conflicting constraints is picked arbitrarily and the others are simply ignored.
The usual way to define the SMIE grammar of a language is by defining a new global variable that holds the precedence table by giving a set of BNF rules. For example, the grammar definition for a small Pascal-like language could look like:
(require 'smie)
(defvar sample-smie-grammar
(smie-prec2->grammar
(smie-bnf->prec2
'((id)
(inst ("begin" insts "end")
("if" exp "then" inst "else" inst)
(id ":=" exp)
(exp))
(insts (insts ";" insts) (inst))
(exp (exp "+" exp)
(exp "*" exp)
("(" exps ")"))
(exps (exps "," exps) (exp)))
'((assoc ";"))
'((assoc ","))
'((assoc "+") (assoc "*")))))
A few things to note:
begin ... end blocks
to appear anywhere anyway.
id has no right hand side: this does not
mean that it can match only the empty string, since as mentioned any
sequence of sexps can appear anywhere anyway.
";" as a statement separator instead,
which SMIE can handle very well.
"," and ";" above)
are best defined with BNF rules such as (foo (foo "separator" foo) ...)
which generate precedence conflicts which are then resolved by giving
them an explicit (assoc "separator").
("(" exps ")") rule was not needed to pair up parens, since
SMIE will pair up any characters that are marked as having paren syntax
in the syntax table. What this rule does instead (together with the
definition of exps) is to make it clear that "," should
not appear outside of parentheses.
left or
right, it is usually preferable to mark operators as associative,
using assoc. For that reason "+" and "*" are
defined above as assoc, although the language defines them
formally as left associative.
SMIE comes with a predefined lexical analyzer which uses syntax tables
in the following way: any sequence of characters that have word or
symbol syntax is considered a token, and so is any sequence of
characters that have punctuation syntax. This default lexer is
often a good starting point but is rarely actually correct for any given
language. For example, it will consider "2,+3" to be composed
of 3 tokens: "2", ",+", and "3".
To describe the lexing rules of your language to SMIE, you need 2 functions, one to fetch the next token, and another to fetch the previous token. Those functions will usually first skip whitespace and comments and then look at the next chunk of text to see if it is a special token. If so it should skip the token and return a description of this token. Usually this is simply the string extracted from the buffer, but it can be anything you want. For example:
(defvar sample-keywords-regexp
(regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "=")))
(defun sample-smie-forward-token ()
(forward-comment (point-max))
(cond
((looking-at sample-keywords-regexp)
(goto-char (match-end 0))
(match-string-no-properties 0))
(t (buffer-substring-no-properties
(point)
(progn (skip-syntax-forward "w_")
(point))))))
(defun sample-smie-backward-token ()
(forward-comment (- (point)))
(cond
((looking-back sample-keywords-regexp (- (point) 2) t)
(goto-char (match-beginning 0))
(match-string-no-properties 0))
(t (buffer-substring-no-properties
(point)
(progn (skip-syntax-backward "w_")
(point))))))
Notice how those lexers return the empty string when in front of parentheses. This is because SMIE automatically takes care of the parentheses defined in the syntax table. More specifically if the lexer returns nil or an empty string, SMIE tries to handle the corresponding text as a sexp according to syntax tables.
The parsing technique used by SMIE does not allow tokens to behave differently in different contexts. For most programming languages, this manifests itself by precedence conflicts when converting the BNF grammar.
Sometimes, those conflicts can be worked around by expressing the grammar slightly differently. For example, for Modula-2 it might seem natural to have a BNF grammar that looks like this:
...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")
("CASE" exp "OF" cases "END")
...)
(cases (cases "|" cases) (caselabel ":" insts) ("ELSE" insts))
...
But this will create conflicts for "ELSE": on the one hand, the
IF rule implies (among many other things) that "ELSE" = "END";
but on the other hand, since "ELSE" appears within cases,
which appears left of "END", we also have "ELSE" > "END".
We can solve the conflict either by using:
...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")
("CASE" exp "OF" cases "END")
("CASE" exp "OF" cases "ELSE" insts "END")
...)
(cases (cases "|" cases) (caselabel ":" insts))
...
or
...
(inst ("IF" exp "THEN" else "END")
("CASE" exp "OF" cases "END")
...)
(else (insts "ELSE" insts))
(cases (cases "|" cases) (caselabel ":" insts) (else))
...
Reworking the grammar to try and solve conflicts has its downsides, tho, because SMIE assumes that the grammar reflects the logical structure of the code, so it is preferable to keep the BNF closer to the intended abstract syntax tree.
Other times, after careful consideration you may conclude that those
conflicts are not serious and simply resolve them via the
resolvers argument of smie-bnf->prec2. Usually this is
because the grammar is simply ambiguous: the conflict does not affect
the set of programs described by the grammar, but only the way those
programs are parsed. This is typically the case for separators and
associative infix operators, where you want to add a resolver like
'((assoc "|")). Another case where this can happen is for the
classic dangling else problem, where you will use '((assoc
"else" "then")). It can also happen for cases where the conflict is
real and cannot really be resolved, but it is unlikely to pose a problem
in practice.
Finally, in many cases some conflicts will remain despite all efforts to
restructure the grammar. Do not despair: while the parser cannot be
made more clever, you can make the lexer as smart as you want. So, the
solution is then to look at the tokens involved in the conflict and to
split one of those tokens into 2 (or more) different tokens. E.g. if
the grammar needs to distinguish between two incompatible uses of the
token "begin", make the lexer return different tokens (say
"begin-fun" and "begin-plain") depending on which kind of
"begin" it finds. This pushes the work of distinguishing the
different cases to the lexer, which will thus have to look at the
surrounding text to find ad-hoc clues.
Based on the provided grammar, SMIE will be able to provide automatic indentation without any extra effort. But in practice, this default indentation style will probably not be good enough. You will want to tweak it in many different cases.
SMIE indentation is based on the idea that indentation rules should be
as local as possible. To this end, it relies on the idea of
virtual indentation, which is the indentation that a particular
program point would have if it were at the beginning of a line.
Of course, if that program point is indeed at the beginning of a line,
its virtual indentation is its current indentation. But if not, then
SMIE uses the indentation algorithm to compute the virtual indentation
of that point. Now in practice, the virtual indentation of a program
point does not have to be identical to the indentation it would have if
we inserted a newline before it. To see how this works, the SMIE rule
for indentation after a { in C does not care whether the
{ is standing on a line of its own or is at the end of the
preceding line. Instead, these different cases are handled in the
indentation rule that decides how to indent before a {.
Another important concept is the notion of parent: The
parent of a token, is the head token of the nearest enclosing
syntactic construct. For example, the parent of an else is the
if to which it belongs, and the parent of an if, in turn,
is the lead token of the surrounding construct. The command
backward-sexp jumps from a token to its parent, but there are
some caveats: for openers (tokens which start a construct, like
if), you need to start with point before the token, while for
others you need to start with point after the token.
backward-sexp stops with point before the parent token if that is
the opener of the token of interest, and otherwise it stops with
point after the parent token.
SMIE indentation rules are specified using a function that takes two arguments method and arg where the meaning of arg and the expected return value depend on method.
method can be:
:after, in which case arg is a token and the function
should return the offset to use for indentation after arg.
:before, in which case arg is a token and the function
should return the offset to use to indent arg itself.
:elem, in which case the function should return either the offset
to use to indent function arguments (if arg is the symbol
arg) or the basic indentation step (if arg is the symbol
basic).
:list-intro, in which case arg is a token and the function
should return non-nil if the token is followed by a list of
expressions (not separated by any token) rather than an expression.
When arg is a token, the function is called with point just before that token. A return value of nil always means to fallback on the default behavior, so the function should return nil for arguments it does not expect.
offset can be:
nil: use the default indentation rule.
(column . column): indent to column column.
:after and its parent for :before.
SMIE provides various functions designed specifically for use in the
indentation rules function (several of those functions break if used in
another context). These functions all start with the prefix
smie-rule-.
Return non-
nilif the current token is hanging. A token is hanging if it is the last token on the line and if it is preceded by other tokens: a lone token on a line is not hanging.
Return non-
nilif the current token's parent is among parents.
Return non-nil if the current token's parent is actually a sibling. This is the case for example when the parent of a
","is just the previous",".
Return the proper offset to align the current token with the parent. If non-
nil, offset should be an integer giving an additional offset to apply.
Indent current token as a separator.
By separator, we mean here a token whose sole purpose is to separate various elements within some enclosing syntactic construct, and which does not have any semantic significance in itself (i.e. it would typically not exist as a node in an abstract syntax tree).
Such a token is expected to have an associative syntax and be closely tied to its syntactic parent. Typical examples are
","in lists of arguments (enclosed inside parentheses), or";"in sequences of instructions (enclosed in a{...}orbegin...endblock).method should be the method name that was passed to `smie-rules-function'.
Here is an example of an indentation function:
(eval-when-compile (require 'cl)) ;For the `case' macro.
(defun sample-smie-rules (kind token)
(case kind
(:elem (case token
(basic sample-indent-basic)))
(:after
(cond
((equal token ",") (smie-rule-separator kind))
((equal token ":=") sample-indent-basic)))
(:before
(cond
((equal token ",") (smie-rule-separator kind))
((member token '("begin" "(" "{"))
(if (smie-rule-hanging-p) (smie-rule-parent)))
((equal token "if")
(and (not (smie-rule-bolp)) (smie-rule-prev-p "else")
(smie-rule-parent)))))))
A few things to note:
sample-indent-basic is nil, then SMIE uses the global
setting smie-indent-basic. The major mode could have set
smie-indent-basic buffer-locally instead, but that
is discouraged.
"," make SMIE try to be
more clever when the comma separator is placed at the beginning of
lines. It tries to outdent the separator so as to align the code after
the comma; for example:
x = longfunctionname (
arg1
, arg2
);
":=" exists because otherwise
SMIE would treat ":=" as an infix operator and would align the
right argument with the left one.
"begin" is an example of the use
of virtual indentation: This rule is used only when "begin" is
hanging, which can happen only when "begin" is not at the
beginning of a line. So this is not used when indenting
"begin" itself but only when indenting something relative to this
"begin". Concretely, this rule changes the indentation from:
if x > 0 then begin
dosomething(x);
end
to
if x > 0 then begin
dosomething(x);
end
"if" is similar to the one for
"begin", but where the purpose is to treat "else if"
as a single unit, so as to align a sequence of tests rather than indent
each test further to the right. This function does this only in the
case where the "if" is not placed on a separate line, hence the
smie-rule-bolp test.
If we know that the "else" is always aligned with its "if"
and is always at the beginning of a line, we can use a more efficient
rule:
((equal token "if")
(and (not (smie-rule-bolp)) (smie-rule-prev-p "else")
(save-excursion
(sample-smie-backward-token) ;Jump before the "else".
(cons 'column (current-column)))))
The advantage of this formulation is that it reuses the indentation of
the previous "else", rather than going all the way back to the
first "if" of the sequence.
Desktop Save Mode is a feature to save the state of Emacs from one session to another. The user-level commands for using Desktop Save Mode are described in the GNU Emacs Manual (see Saving Emacs Sessions). Modes whose buffers visit a file, don't have to do anything to use this feature.
For buffers not visiting a file to have their state saved, the major
mode must bind the buffer local variable desktop-save-buffer to
a non-nil value.
If this buffer-local variable is non-
nil, the buffer will have its state saved in the desktop file at desktop save. If the value is a function, it is called at desktop save with argument desktop-dirname, and its value is saved in the desktop file along with the state of the buffer for which it was called. When file names are returned as part of the auxiliary information, they should be formatted using the call(desktop-file-name file-name desktop-dirname)
For buffers not visiting a file to be restored, the major mode must
define a function to do the job, and that function must be listed in
the alist desktop-buffer-mode-handlers.
Alist with elements
(major-mode . restore-buffer-function)The function restore-buffer-function will be called with argument list
(buffer-file-name buffer-name desktop-buffer-misc)and it should return the restored buffer. Here desktop-buffer-misc is the value returned by the function optionally bound to
desktop-save-buffer.
GNU Emacs Lisp has convenient on-line help facilities, most of which derive their information from the documentation strings associated with functions and variables. This chapter describes how to write good documentation strings for your Lisp programs, as well as how to write programs to access documentation.
Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion.
For commands to display documentation strings, see Help. For the conventions for writing documentation strings, see Documentation Tips.
A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text of the string. This is because it really is a Lisp string object. The string serves as documentation when it is written in the proper place in the definition of a function or variable. In a function definition, the documentation string follows the argument list. In a variable definition, the documentation string follows the initial value of the variable.
When you write a documentation string, make the first line a
complete sentence (or two complete sentences) since some commands,
such as apropos, show only the first line of a multi-line
documentation string. Also, you should not indent the second line of
a documentation string, if it has one, because that looks odd when you
use C-h f (describe-function) or C-h v
(describe-variable) to view the documentation string. There
are many other conventions for doc strings; see Documentation Tips.
Documentation strings can contain several special substrings, which stand for key bindings to be looked up in the current keymaps when the documentation is displayed. This allows documentation strings to refer to the keys for related commands and be accurate even when a user rearranges the key bindings. (See Keys in Documentation.)
Emacs Lisp mode fills documentation strings to the width
specified by emacs-lisp-docstring-fill-column.
In Emacs Lisp, a documentation string is accessible through the function or variable that it describes:
documentation knows how to extract it. You can also put
function documentation in the function-documentation property
of the function name. That is useful with definitions such as
keyboard macros that can't hold a documentation string.
variable-documentation. The
function documentation-property knows how to retrieve it.
To save space, the documentation for preloaded functions and variables (including primitive functions and autoloaded functions) is stored in the file emacs/etc/DOC-version—not inside Emacs. The documentation strings for functions and variables loaded during the Emacs session from byte-compiled files are stored in those files (see Docs and Compilation).
The data structure inside Emacs has an integer offset into the file, or
a list containing a file name and an integer, in place of the
documentation string. The functions documentation and
documentation-property use that information to fetch the
documentation string from the appropriate file; this is transparent to
the user.
The emacs/lib-src directory contains two utilities that you can use to print nice-looking hardcopy for the file emacs/etc/DOC-version. These are sorted-doc and digest-doc.
This function returns the documentation string that is recorded in symbol's property list under property property. It retrieves the text from a file if the value calls for that. If the property value isn't
nil, isn't a string, and doesn't refer to text in a file, then it is evaluated to obtain a string.The last thing this function does is pass the string through
substitute-command-keysto substitute actual key bindings, unless verbatim is non-nil.(documentation-property 'command-line-processed 'variable-documentation) ⇒ "Non-nil once command line has been processed" (symbol-plist 'command-line-processed) ⇒ (variable-documentation 188902) (documentation-property 'emacs 'group-documentation) ⇒ "Customization of the One True Editor."
This function returns the documentation string of function.
documentationhandles macros, named keyboard macros, and special forms, as well as ordinary functions.If function is a symbol, this function first looks for the
function-documentationproperty of that symbol; if that has a non-nilvalue, the documentation comes from that value (if the value is not a string, it is evaluated). If function is not a symbol, or if it has nofunction-documentationproperty, thendocumentationextracts the documentation string from the actual function definition, reading it from a file if called for.Finally, unless verbatim is non-
nil, it callssubstitute-command-keysso as to return a value containing the actual (current) key bindings.The function
documentationsignals avoid-functionerror if function has no function definition. However, it is OK if the function definition has no documentation string. In that case,documentationreturnsnil.
This function returns the documentation string of face as a face.
Here is an example of using the two functions, documentation and
documentation-property, to display the documentation strings for
several symbols in a ‘*Help*’ buffer.
(defun describe-symbols (pattern)
"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the `*Help*' buffer."
(interactive "sDescribe symbols matching: ")
(let ((describe-func
(function
(lambda (s)
;; Print description of symbol.
(if (fboundp s) ; It is a function.
(princ
(format "%s\t%s\n%s\n\n" s
(if (commandp s)
(let ((keys (where-is-internal s)))
(if keys
(concat
"Keys: "
(mapconcat 'key-description
keys " "))
"Keys: none"))
"Function")
(or (documentation s)
"not documented"))))
(if (boundp s) ; It is a variable.
(princ
(format "%s\t%s\n%s\n\n" s
(if (user-variable-p s)
"Option " "Variable")
(or (documentation-property
s 'variable-documentation)
"not documented")))))))
sym-list)
;; Build a list of symbols that match pattern.
(mapatoms (function
(lambda (sym)
(if (string-match pattern (symbol-name sym))
(setq sym-list (cons sym sym-list))))))
;; Display the data.
(help-setup-xref (list 'describe-symbols pattern) (interactive-p))
(with-help-window (help-buffer)
(mapcar describe-func (sort sym-list 'string<)))))
The describe-symbols function works like apropos,
but provides more information.
(describe-symbols "goal")
---------- Buffer: *Help* ----------
goal-column Option
Semipermanent goal column for vertical motion, as set by ...
set-goal-column Keys: C-x C-n
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved to
rather than trying to keep the same horizontal position.
With a non-nil argument, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable `goal-column'.
temporary-goal-column Variable
Current goal column for vertical motion.
It is the column where point was
at the start of current run of vertical motion commands.
When the `track-eol' feature is doing its job, the value is 9999.
---------- Buffer: *Help* ----------
This function is used only during Emacs initialization, just before the runnable Emacs is dumped. It finds the file offsets of the documentation strings stored in the file filename, and records them in the in-core function definitions and variable property lists in place of the actual strings. See Building Emacs.
Emacs reads the file filename from the emacs/etc directory. When the dumped Emacs is later executed, the same file will be looked for in the directory
doc-directory. Usually filename is"DOC-version".
This variable holds the name of the directory which should contain the file
"DOC-version"that contains documentation strings for built-in and preloaded functions and variables.In most cases, this is the same as
data-directory. They may be different when you run Emacs from the directory where you built it, without actually installing it. See Definition of data-directory.
When documentation strings refer to key sequences, they should use the
current, actual key bindings. They can do so using certain special text
sequences described below. Accessing documentation strings in the usual
way substitutes current key binding information for these special
sequences. This works by calling substitute-command-keys. You
can also call that function yourself.
Here is a list of the special sequences and what they mean:
\[command]\{mapvar}describe-bindings.
\<mapvar>\=Please note: Each ‘\’ must be doubled when written in a string in Emacs Lisp.
This function scans string for the above special sequences and replaces them by what they stand for, returning the result as a string. This permits display of documentation that refers accurately to the user's own customized key bindings.
Here are examples of the special sequences:
(substitute-command-keys
"To abort recursive edit, type: \\[abort-recursive-edit]")
⇒ "To abort recursive edit, type: C-]"
(substitute-command-keys
"The keys that are defined for the minibuffer here are:
\\{minibuffer-local-must-match-map}")
⇒ "The keys that are defined for the minibuffer here are:
? minibuffer-completion-help
SPC minibuffer-complete-word
TAB minibuffer-complete
C-j minibuffer-complete-and-exit
RET minibuffer-complete-and-exit
C-g abort-recursive-edit
"
(substitute-command-keys
"To abort a recursive edit from the minibuffer, type\
\\<minibuffer-local-must-match-map>\\[abort-recursive-edit].")
⇒ "To abort a recursive edit from the minibuffer, type C-g."
There are other special conventions for the text in documentation strings—for instance, you can refer to functions, variables, and sections of this manual. See Documentation Tips, for details.
These functions convert events, key sequences, or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself.
This function returns a string containing the Emacs standard notation for the input events in sequence. If prefix is non-
nil, it is a sequence of input events leading up to sequence and is included in the return value. Both arguments may be strings, vectors or lists. See Input Events, for more information about valid events.(key-description [?\M-3 delete]) ⇒ "M-3 <delete>" (key-description [delete] "\M-3") ⇒ "M-3 <delete>"See also the examples for
single-key-description, below.
This function returns a string describing event in the standard Emacs notation for keyboard input. A normal printing character appears as itself, but a control character turns into a string starting with ‘C-’, a meta character turns into a string starting with ‘M-’, and space, tab, etc. appear as ‘SPC’, ‘TAB’, etc. A function key symbol appears inside angle brackets ‘<...>’. An event that is a list appears as the name of the symbol in the car of the list, inside angle brackets.
If the optional argument no-angles is non-
nil, the angle brackets around function keys and event symbols are omitted; this is for compatibility with old versions of Emacs which didn't use the brackets.(single-key-description ?\C-x) ⇒ "C-x" (key-description "\C-x \M-y \n \t \r \f123") ⇒ "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" (single-key-description 'delete) ⇒ "<delete>" (single-key-description 'C-mouse-1) ⇒ "<C-mouse-1>" (single-key-description 'C-mouse-1 t) ⇒ "C-mouse-1"
This function returns a string describing character in the standard Emacs notation for characters that appear in text—like
single-key-description, except that control characters are represented with a leading caret (which is how control characters in Emacs buffers are usually displayed). Another difference is thattext-char-descriptionrecognizes the 2**7 bit as the Meta character, whereassingle-key-descriptionuses the 2**27 bit for Meta.(text-char-description ?\C-c) ⇒ "^C" (text-char-description ?\M-m) ⇒ "\xed" (text-char-description ?\C-\M-m) ⇒ "\x8d" (text-char-description (+ 128 ?m)) ⇒ "M-m" (text-char-description (+ 128 ?\C-m)) ⇒ "M-^M"
This function is used mainly for operating on keyboard macros, but it can also be used as a rough inverse for
key-description. You call it with a string containing key descriptions, separated by spaces; it returns a string or vector containing the corresponding events. (This may or may not be a single valid key sequence, depending on what events you use; see Key Sequences.) If need-vector is non-nil, the return value is always a vector.
Emacs provides a variety of on-line help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see Help. Here we describe some program-level interfaces to the same information.
This function finds all “meaningful” symbols whose names contain a match for the apropos pattern pattern. An apropos pattern is either a word to match, a space-separated list of words of which at least two must match, or a regular expression (if any special regular expression characters occur). A symbol is “meaningful” if it has a definition as a function, variable, or face, or has properties.
The function returns a list of elements that look like this:
(symbol score fn-doc var-doc plist-doc widget-doc face-doc group-doc)Here, score is an integer measure of how important the symbol seems to be as a match, and the remaining elements are documentation strings for symbol's various roles (or
nil).It also displays the symbols in a buffer named ‘*Apropos*’, each with a one-line description taken from the beginning of its documentation string.
If do-all is non-
nil, or if the user optionapropos-do-allis non-nil, thenaproposalso shows key bindings for the functions that are found; it also shows all interned symbols, not just meaningful ones (and it lists them in the return value as well).
The value of this variable is a local keymap for characters following the Help key, C-h.
This symbol is not a function; its function definition cell holds the keymap known as
help-map. It is defined in help.el as follows:(define-key global-map (string help-char) 'help-command) (fset 'help-command help-map)
The value of this variable is the help character—the character that Emacs recognizes as meaning Help. By default, its value is 8, which stands for C-h. When Emacs reads this character, if
help-formis a non-nilLisp expression, it evaluates that expression, and displays the result in a window if it is a string.Usually the value of
help-formisnil. Then the help character has no special meaning at the level of command input, and it becomes part of a key sequence in the normal way. The standard key binding of C-h is a prefix key for several general-purpose help features.The help character is special after prefix keys, too. If it has no binding as a subcommand of the prefix key, it runs
describe-prefix-bindings, which displays a list of all the subcommands of the prefix key.
The value of this variable is a list of event types that serve as alternative “help characters.” These events are handled just like the event specified by
help-char.
If this variable is non-
nil, its value is a form to evaluate whenever the characterhelp-charis read. If evaluating the form produces a string, that string is displayed.A command that calls
read-eventorread-charprobably should bindhelp-formto a non-nilexpression while it does input. (The time when you should not do this is when C-h has some other meaning.) Evaluating this expression should result in a string that explains what the input is for and how to enter it properly.Entry to the minibuffer binds this variable to the value of
minibuffer-help-form(see Definition of minibuffer-help-form).
This variable holds a function to print help for a prefix key. The function is called when the user types a prefix key followed by the help character, and the help character has no binding after that prefix. The variable's default value is
describe-prefix-bindings.
This function calls
describe-bindingsto display a list of all the subcommands of the prefix key of the most recent key sequence. The prefix described consists of all but the last event of that key sequence. (The last event is, presumably, the help character.)
The following two functions are meant for modes that want to provide help without relinquishing control, such as the “electric” modes. Their names begin with ‘Helper’ to distinguish them from the ordinary help functions.
This command pops up a window displaying a help buffer containing a listing of all of the key bindings from both the local and global keymaps. It works by calling
describe-bindings.
This command provides help for the current mode. It prompts the user in the minibuffer with the message ‘Help (Type ? for further options)’, and then provides assistance in finding out what the key bindings are, and what the mode is intended for. It returns
nil.This can be customized by changing the map
Helper-help-map.
This variable holds the name of the directory in which Emacs finds certain documentation and text files that come with Emacs.
This function returns the name of the help buffer, which is normally ‘*Help*’; if such a buffer does not exist, it is first created.
This macro evaluates the body forms, inserting any output they produce into a buffer named buffer-name like
with-output-to-temp-buffer(see Temporary Displays). (Usually, buffer-name should be the value returned by the functionhelp-buffer.) It also puts the specified buffer into Help mode and displays a message telling the user how to quit and scroll the help window.
This function updates the cross reference data in the ‘*Help*’ buffer, which is used to regenerate the help information when the user clicks on the ‘Back’ or ‘Forward’ buttons. Most commands that use the ‘*Help*’ buffer should invoke this function before clearing the buffer. The item argument should have the form
(funtion.args), where funtion is a function to call, with argument list args, to regenerate the help buffer. The interactive-p argument is non-nilif the calling command was invoked interactively; in that case, the stack of items for the ‘*Help*’ buffer's ‘Back’ buttons is cleared.
See describe-symbols example, for an example of using
help-buffer, with-help-window, and
help-setup-xref.
This macro defines a help command named fname that acts like a prefix key that shows a list of the subcommands it offers.
When invoked, fname displays help-text in a window, then reads and executes a key sequence according to help-map. The string help-text should describe the bindings available in help-map.
The command fname is defined to handle a few events itself, by scrolling the display of help-text. When fname reads one of those special events, it does the scrolling and then reads another event. When it reads an event that is not one of those few, and which has a binding in help-map, it executes that key's binding and then returns.
The argument help-line should be a single-line summary of the alternatives in help-map. In the current version of Emacs, this argument is used only if you set the option
three-step-helptot.This macro is used in the command
help-for-helpwhich is the binding of C-h C-h.
If this variable is non-
nil, commands defined withmake-help-screendisplay their help-line strings in the echo area at first, and display the longer help-text strings only if the user types the help character again.
In Emacs, you can find, create, view, save, and otherwise work with files and file directories. This chapter describes most of the file-related functions of Emacs Lisp, but a few others are described in Buffers, and those related to backups and auto-saving are described in Backups and Auto-Saving.
Many of the file functions take one or more arguments that are file
names. A file name is actually a string. Most of these functions
expand file name arguments by calling expand-file-name, so that
~ is handled correctly, as are relative file names (including
‘../’). These functions don't recognize environment variable
substitutions such as ‘$HOME’. See File Name Expansion.
When file I/O functions signal Lisp errors, they usually use the
condition file-error (see Handling Errors). The error
message is in most cases obtained from the operating system, according
to locale system-message-locale, and decoded using coding system
locale-coding-system (see Locales).
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file “the visited file” of the buffer.
A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). Usually, a buffer contains information that you have copied from a file; then we say the buffer is visiting that file. The copy in the buffer is what you modify with editing commands. Such changes to the buffer do not change the file; therefore, to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.
In spite of the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, “I am editing a file,” rather than, “I am editing a buffer that I will soon save as a file of the same name.” Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind.
This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with ‘find-’ rather than ‘visit-’. See Buffer File Name, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.
In a Lisp program, if you want to look at the contents of a file but
not alter it, the fastest way is to use insert-file-contents in a
temporary buffer. Visiting the file is not necessary and takes longer.
See Reading from Files.
This command selects a buffer visiting the file filename, using an existing buffer if there is one, and otherwise creating a new buffer and reading the file into it. It also returns that buffer.
Aside from some technical details, the body of the
find-filefunction is basically equivalent to:(switch-to-buffer (find-file-noselect filename nil nil wildcards))(See
switch-to-bufferin Displaying Buffers.)If wildcards is non-
nil, which is always true in an interactive call, thenfind-fileexpands wildcard characters in filename and visits all the matching files.When
find-fileis called interactively, it prompts for filename in the minibuffer.
This command visits filename, like
find-filedoes, but it does not perform any format conversions (see Format Conversion), character code conversions (see Coding Systems), or end-of-line conversions (see End of line conversion). The buffer visiting the file is made unibyte, and its major mode is Fundamental mode, regardless of the file name. File local variable specifications in the file (see File Local Variables) are ignored, and automatic decompression and adding a newline at the end of the file due torequire-final-newline(see require-final-newline) are also disabled.Note that if Emacs already has a buffer visiting the same file non-literally, it will not visit the same file literally, but instead just switch to the existing buffer. If you want to be sure of accessing a file's contents literally, you should create a temporary buffer and then read the file contents into it using
insert-file-contents-literally(see Reading from Files).
This function is the guts of all the file-visiting functions. It returns a buffer visiting the file filename. You may make the buffer current or display it in a window if you wish, but this function does not do so.
The function returns an existing buffer if there is one; otherwise it creates a new buffer and reads the file into it. When
find-file-noselectuses an existing buffer, it first verifies that the file has not changed since it was last visited or saved in that buffer. If the file has changed, this function asks the user whether to reread the changed file. If the user says ‘yes’, any edits previously made in the buffer are lost.Reading the file involves decoding the file's contents (see Coding Systems), including end-of-line conversion, and format conversion (see Format Conversion). If wildcards is non-
nil, thenfind-file-noselectexpands wildcard characters in filename and visits all the matching files.This function displays warning or advisory messages in various peculiar cases, unless the optional argument nowarn is non-
nil. For example, if it needs to create a buffer, and there is no file named filename, it displays the message ‘(New file)’ in the echo area, and leaves the buffer empty.The
find-file-noselectfunction normally callsafter-find-fileafter reading the file (see Subroutines of Visiting). That function sets the buffer major mode, parses local variables, warns the user if there exists an auto-save file more recent than the file just visited, and finishes by running the functions infind-file-hook.If the optional argument rawfile is non-
nil, thenafter-find-fileis not called, and thefind-file-not-found-functionsare not run in case of failure. What's more, a non-nilrawfile value suppresses coding system conversion and format conversion.The
find-file-noselectfunction usually returns the buffer that is visiting the file filename. But, if wildcards are actually used and expanded, it returns a list of buffers that are visiting the various files.(find-file-noselect "/etc/fstab") ⇒ #<buffer fstab>
This command selects a buffer visiting the file filename, but does so in a window other than the selected window. It may use another existing window or split a window; see Displaying Buffers.
When this command is called interactively, it prompts for filename.
This command selects a buffer visiting the file filename, like
find-file, but it marks the buffer as read-only. See Read Only Buffers, for related functions and variables.When this command is called interactively, it prompts for filename.
This command visits filename using View mode, returning to the previous buffer when you exit View mode. View mode is a minor mode that provides commands to skim rapidly through the file, but does not let you modify the text. Entering View mode runs the normal hook
view-mode-hook. See Hooks.When
view-fileis called interactively, it prompts for filename.
If this variable is non-
nil, then the variousfind-filecommands check for wildcard characters and visit all the files that match them (when invoked interactively or when their wildcards argument is non-nil). If this option isnil, then thefind-filecommands ignore their wildcards argument and never treat wildcard characters specially.
The value of this variable is a list of functions to be called after a file is visited. The file's local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run.
This variable is a normal hook. See Hooks.
The value of this variable is a list of functions to be called when
find-fileorfind-file-noselectis passed a nonexistent file name.find-file-noselectcalls these functions as soon as it detects a nonexistent file. It calls them in the order of the list, until one of them returns non-nil.buffer-file-nameis already set up.This is not a normal hook because the values of the functions are used, and in many cases only some of the functions are called.
This buffer-local variable, if set to a non-
nilvalue, makessave-bufferbehave as if the buffer were visiting its file literally, i.e. without conversions of any kind. The commandfind-file-literallysets this variable's local value, but other equivalent functions and commands can do that as well, e.g. to avoid automatic addition of a newline at the end of the file. This variable us permanent local, so it is unaffected by changes of major modes.
The find-file-noselect function uses two important subroutines
which are sometimes useful in user Lisp code: create-file-buffer
and after-find-file. This section explains how to use them.
This function creates a suitably named buffer for visiting filename, and returns it. It uses filename (sans directory) as the name if that name is free; otherwise, it appends a string such as ‘<2>’ to get an unused name. See also Creating Buffers.
Please note:
create-file-bufferdoes not associate the new buffer with a file and does not select the buffer. It also does not use the default major mode.(create-file-buffer "foo") ⇒ #<buffer foo> (create-file-buffer "foo") ⇒ #<buffer foo<2>> (create-file-buffer "foo") ⇒ #<buffer foo<3>>This function is used by
find-file-noselect. It usesgenerate-new-buffer(see Creating Buffers).
This function sets the buffer major mode, and parses local variables (see Auto Major Mode). It is called by
find-file-noselectand by the default revert function (see Reverting).If reading the file got an error because the file does not exist, but its directory does exist, the caller should pass a non-
nilvalue for error. In that case,after-find-fileissues a warning: ‘(New file)’. For more serious errors, the caller should usually not callafter-find-file.If warn is non-
nil, then this function issues a warning if an auto-save file exists and is more recent than the visited file.If noauto is non-
nil, that says not to enable or disable Auto-Save mode. The mode remains enabled if it was enabled before.If after-find-file-from-revert-buffer is non-
nil, that means this call was fromrevert-buffer. This has no direct effect, but some mode functions and hook functions check the value of this variable.If nomodes is non-
nil, that means don't alter the buffer's major mode, don't process local variables specifications in the file, and don't runfind-file-hook. This feature is used byrevert-bufferin some cases.The last thing
after-find-filedoes is call all the functions in the listfind-file-hook.
When you edit a file in Emacs, you are actually working on a buffer that is visiting that file—that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing.
save-bufferis responsible for making backup files. Normally, backup-option isnil, andsave-buffermakes a backup file only if this is the first save since visiting the file. Other values for backup-option request the making of backup files in other circumstances:
- With an argument of 4 or 64, reflecting 1 or 3 C-u's, the
save-bufferfunction marks this version of the file to be backed up when the buffer is next saved.- With an argument of 16 or 64, reflecting 2 or 3 C-u's, the
save-bufferfunction unconditionally backs up the previous version of the file before saving it.- With an argument of 0, unconditionally do not make any backup file.
This command saves some modified file-visiting buffers. Normally it asks the user about each buffer. But if save-silently-p is non-
nil, it saves all the file-visiting buffers without querying the user.The optional pred argument controls which buffers to ask about (or to save silently if save-silently-p is non-
nil). If it isnil, that means to ask only about file-visiting buffers. If it ist, that means also offer to save certain other non-file buffers—those that have a non-nilbuffer-local value ofbuffer-offer-save(see Killing Buffers). A user who says ‘yes’ to saving a non-file buffer is asked to specify the file name to use. Thesave-buffers-kill-emacsfunction passes the valuetfor pred.If pred is neither
tnornil, then it should be a function of no arguments. It will be called in each buffer to decide whether to offer to save that buffer. If it returns a non-nilvalue in a certain buffer, that means do offer to save that buffer.
This function writes the current buffer into file filename, makes the buffer visit that file, and marks it not modified. Then it renames the buffer based on filename, appending a string like ‘<2>’ if necessary to make a unique buffer name. It does most of this work by calling
set-visited-file-name(see Buffer File Name) andsave-buffer.If confirm is non-
nil, that means to ask for confirmation before overwriting an existing file. Interactively, confirmation is required, unless the user supplies a prefix argument.If filename is an existing directory, or a symbolic link to one,
write-fileuses the name of the visited file, in directory filename. If the buffer is not visiting a file, it uses the buffer name instead.
Saving a buffer runs several hooks. It also performs format conversion (see Format Conversion).
The value of this variable is a list of functions to be called before writing out a buffer to its visited file. If one of them returns non-
nil, the file is considered already written and the rest of the functions are not called, nor is the usual code for writing the file executed.If a function in
write-file-functionsreturns non-nil, it is responsible for making a backup file (if that is appropriate). To do so, execute the following code:(or buffer-backed-up (backup-buffer))You might wish to save the file modes value returned by
backup-bufferand use that (if non-nil) to set the mode bits of the file that you write. This is whatsave-buffernormally does. See Making Backup Files.The hook functions in
write-file-functionsare also responsible for encoding the data (if desired): they must choose a suitable coding system and end-of-line conversion (see Lisp and Coding Systems), perform the encoding (see Explicit Encoding), and setlast-coding-system-usedto the coding system that was used (see Encoding and I/O).If you set this hook locally in a buffer, it is assumed to be associated with the file or the way the contents of the buffer were obtained. Thus the variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. On the other hand, calling
set-visited-file-namewill reset it. If this is not what you want, you might like to usewrite-contents-functionsinstead.Even though this is not a normal hook, you can use
add-hookandremove-hookto manipulate the list. See Hooks.
This works just like
write-file-functions, but it is intended for hooks that pertain to the buffer's contents, not to the particular visited file or its location. Such hooks are usually set up by major modes, as buffer-local bindings for this variable. This variable automatically becomes buffer-local whenever it is set; switching to a new major mode always resets this variable, but callingset-visited-file-namedoes not.If any of the functions in this hook returns non-
nil, the file is considered already written and the rest are not called and neither are the functions inwrite-file-functions.
This normal hook runs before a buffer is saved in its visited file, regardless of whether that is done normally or by one of the hooks described above. For instance, the copyright.el program uses this hook to make sure the file you are saving has the current year in its copyright notice.
This normal hook runs after a buffer has been saved in its visited file. One use of this hook is in Fast Lock mode; it uses this hook to save the highlighting information in a cache file.
If this variable is non-
nil, thensave-bufferprotects against I/O errors while saving by writing the new file to a temporary name instead of the name it is supposed to have, and then renaming it to the intended name after it is clear there are no errors. This procedure prevents problems such as a lack of disk space from resulting in an invalid file.As a side effect, backups are necessarily made by copying. See Rename or Copy. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names.
Some modes give this variable a non-
nilbuffer-local value in particular buffers.
This variable determines whether files may be written out that do not end with a newline. If the value of the variable is
t, thensave-buffersilently adds a newline at the end of the file whenever the buffer being saved does not already end in one. If the value of the variable is non-nil, but nott, thensave-bufferasks the user whether to add a newline each time the case arises.If the value of the variable is
nil, thensave-bufferdoesn't add newlines at all.nilis the default value, but a few major modes set it totin particular buffers.
See also the function set-visited-file-name (see Buffer File Name).
You can copy a file from the disk and insert it into a buffer
using the insert-file-contents function. Don't use the user-level
command insert-file in a Lisp program, as that sets the mark.
This function inserts the contents of file filename into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if filename is not the name of a file that can be read.
The function
insert-file-contentschecks the file contents against the defined file formats, and converts the file contents if appropriate and also calls the functions in the listafter-insert-file-functions. See Format Conversion. Normally, one of the functions in theafter-insert-file-functionslist determines the coding system (see Coding Systems) used for decoding the file's contents, including end-of-line conversion. However, if the file contains null bytes, it is by default visited without any code conversions; see inhibit-null-byte-detection, for how to control this behavior.If visit is non-
nil, this function additionally marks the buffer as unmodified and sets up various fields in the buffer so that it is visiting the file filename: these include the buffer's visited file name and its last save file modtime. This feature is used byfind-file-noselectand you probably should not use it yourself.If beg and end are non-
nil, they should be integers specifying the portion of the file to insert. In this case, visit must benil. For example,(insert-file-contents filename nil 0 500)inserts the first 500 characters of a file.
If the argument replace is non-
nil, it means to replace the contents of the buffer (actually, just the accessible portion) with the contents of the file. This is better than simply deleting the buffer contents and inserting the whole file, because (1) it preserves some marker positions and (2) it puts less data in the undo list.It is possible to read a special file (such as a FIFO or an I/O device) with
insert-file-contents, as long as replace and visit arenil.
This function works like
insert-file-contentsexcept that it does not do format decoding (see Format Conversion), does not do character code conversion (see Coding Systems), does not runfind-file-hook, does not perform automatic uncompression, and so on.
If you want to pass a file name to another process so that another
program can read the file, use the function file-local-copy; see
Magic File Names.
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the append-to-file and
write-region functions. Don't use these functions to write to
files that are being visited; that could cause confusion in the
mechanisms for visiting.
This function appends the contents of the region delimited by start and end in the current buffer to the end of file filename. If that file does not exist, it is created. This function returns
nil.An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
When called from Lisp, this function is completely equivalent to:
(write-region start end filename t)
This function writes the region delimited by start and end in the current buffer into the file specified by filename.
If start is
nil, then the command writes the entire buffer contents (not just the accessible portion) to the file and ignores end.If start is a string, then
write-regionwrites or appends that string, rather than text from the buffer. end is ignored in this case.If append is non-
nil, then the specified text is appended to the existing file contents (if any). If append is an integer,write-regionseeks to that byte offset from the start of the file and writes the data from there.If mustbenew is non-
nil, thenwrite-regionasks for confirmation if filename names an existing file. If mustbenew is the symbolexcl, thenwrite-regiondoes not ask for confirmation, but instead it signals an errorfile-already-existsif the file already exists.The test for an existing file, when mustbenew is
excl, uses a special system feature. At least for files on a local disk, there is no chance that some other program could create a file of the same name before Emacs does, without Emacs's noticing.If visit is
t, then Emacs establishes an association between the buffer and the file: the buffer is then visiting that file. It also sets the last file modification time for the current buffer to filename's modtime, and marks the buffer as not modified. This feature is used bysave-buffer, but you probably should not use it yourself.If visit is a string, it specifies the file name to visit. This way, you can write the data to one file (filename) while recording the buffer as visiting another file (visit). The argument visit is used in the echo area message and also for file locking; visit is stored in
buffer-file-name. This feature is used to implementfile-precious-flag; don't use it yourself unless you really know what you're doing.The optional argument lockname, if non-
nil, specifies the file name to use for purposes of locking and unlocking, overriding filename and visit for that purpose.The function
write-regionconverts the data which it writes to the appropriate file formats specified bybuffer-file-formatand also calls the functions in the listwrite-region-annotate-functions. See Format Conversion.Normally,
write-regiondisplays the message ‘Wrote filename’ in the echo area. If visit is neithertnornilnor a string, then this message is inhibited. This feature is useful for programs that use files for internal purposes, files that the user does not need to know about.
The
with-temp-filemacro evaluates the body forms with a temporary buffer as the current buffer; then, at the end, it writes the buffer contents into file file. It kills the temporary buffer when finished, restoring the buffer that was current before thewith-temp-fileform. Then it returns the value of the last form in body.The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).See also
with-temp-bufferin The Current Buffer.
When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. (File locks are not implemented on Microsoft systems.) Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do. The file lock is really a file, a symbolic link with a special name, stored in the same directory as the file you are editing.
When you access files using NFS, there may be a small probability that you and another user will both lock the same file “simultaneously.” If this happens, it is possible for the two users to make changes simultaneously, but Emacs will still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see Modification Time.
This function returns
nilif the file filename is not locked. It returnstif it is locked by this Emacs process, and it returns the name of the user who has locked it if it is locked by some other job.(file-locked-p "foo") ⇒ nil
This function locks the file filename, if the current buffer is modified. The argument filename defaults to the current buffer's visited file. Nothing is done if the current buffer is not visiting a file, or is not modified, or if the system does not support locking.
This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file, or if the system does not support locking.
File locking is not supported on some systems. On systems that do not
support it, the functions lock-buffer, unlock-buffer and
file-locked-p do nothing and return nil.
This function is called when the user tries to modify file, but it is locked by another user named other-user. The default definition of this function asks the user to say what to do. The value this function returns determines what Emacs does next:
- A value of
tsays to grab the lock on the file. Then this user may edit the file and other-user loses the lock.- A value of
nilsays to ignore the lock and let this user edit the file anyway.- This function may instead signal a
file-lockederror, in which case the change that the user was about to make does not take place.The error message for this error looks like this:
error--> File is locked: file other-userwhere
fileis the name of the file and other-user is the name of the user who has locked the file.If you wish, you can replace the
ask-user-about-lockfunction with your own version that makes the decision in another way. The code for its usual definition is in userlock.el.
The functions described in this section all operate on strings that designate file names. With a few exceptions, all the functions have names that begin with the word ‘file’. These functions all return information about actual files or directories, so their arguments must all exist as actual files or directories unless otherwise noted.
These functions test for permission to access a file in specific ways. Unless explicitly stated otherwise, they recursively follow symbolic links for their file name arguments, at all levels (at the level of the file itself and at all levels of parent directories).
This function returns
tif a file named filename appears to exist. This does not mean you can necessarily read the file, only that you can find out its attributes. (On Unix and GNU/Linux, this is true if the file exists and you have execute permission on the containing directories, regardless of the protection of the file itself.)If the file does not exist, or if fascist access control policies prevent you from finding the attributes of the file, this function returns
nil.Directories are files, so
file-exists-preturnstwhen given a directory name. However, symbolic links are treated specially;file-exists-preturnstfor a symbolic link name only if the target file exists.
This function returns
tif a file named filename exists and you can read it. It returnsnilotherwise.(file-readable-p "files.texi") ⇒ t (file-exists-p "/usr/spool/mqueue") ⇒ t (file-readable-p "/usr/spool/mqueue") ⇒ nil
This function returns
tif a file named filename exists and you can execute it. It returnsnilotherwise. On Unix and GNU/Linux, if the file is a directory, execute permission means you can check the existence and attributes of files inside the directory, and open those files if their modes permit.
This function returns
tif the file filename can be written or created by you, andnilotherwise. A file is writable if the file exists and you can write it. It is creatable if it does not exist, but the specified directory does exist and you can write in that directory.In the third example below, foo is not writable because the parent directory does not exist, even though the user could create such a directory.
(file-writable-p "~/foo") ⇒ t (file-writable-p "/foo") ⇒ nil (file-writable-p "~/no-such-dir/foo") ⇒ nil
This function returns
tif you have permission to open existing files in the directory whose name as a file is dirname; otherwise (or if there is no such directory), it returnsnil. The value of dirname may be either a directory name (such as /foo/) or the file name of a file which is a directory (such as /foo, without the final slash).Example: after the following,
(file-accessible-directory-p "/foo") ⇒ nilwe can deduce that any attempt to read a file in /foo/ will give an error.
This function opens file filename for reading, then closes it and returns
nil. However, if the open fails, it signals an error using string as the error message text.
This function returns
tif deleting the file filename and then creating it anew would keep the file's owner unchanged. It also returnstfor nonexistent files.If filename is a symbolic link, then, unlike the other functions discussed here,
file-ownership-preserved-pdoes not replace filename with its target. However, it does recursively follow symbolic links at all levels of parent directories.
This function returns
tif the file filename1 is newer than file filename2. If filename1 does not exist, it returnsnil. If filename1 does exist, but filename2 does not, it returnst.In the following example, assume that the file aug-19 was written on the 19th, aug-20 was written on the 20th, and the file no-file doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20") ⇒ nil (file-newer-than-file-p "aug-20" "aug-19") ⇒ t (file-newer-than-file-p "aug-19" "no-file") ⇒ t (file-newer-than-file-p "no-file" "aug-19") ⇒ nilYou can use
file-attributesto get a file's last modification time as a list of two numbers. See File Attributes.
This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files.
If the file filename is a symbolic link, the
file-symlink-pfunction returns the (non-recursive) link target as a string. (Determining the file name that the link points to from the target is nontrivial.) First, this function recursively follows symbolic links at all levels of parent directories.If the file filename is not a symbolic link (or there is no such file),
file-symlink-preturnsnil.(file-symlink-p "foo") ⇒ nil (file-symlink-p "sym-link") ⇒ "foo" (file-symlink-p "sym-link2") ⇒ "sym-link" (file-symlink-p "/bin") ⇒ "/pub/bin"
The next two functions recursively follow symbolic links at all levels for filename.
This function returns
tif filename is the name of an existing directory,nilotherwise.(file-directory-p "~rms") ⇒ t (file-directory-p "~rms/lewis/files.texi") ⇒ nil (file-directory-p "~rms/lewis/no-such-file") ⇒ nil (file-directory-p "$HOME") ⇒ nil (file-directory-p (substitute-in-file-name "$HOME")) ⇒ t
This function returns
tif the file filename exists and is a regular file (not a directory, named pipe, terminal, or other I/O device).
The truename of a file is the name that you get by following symbolic links at all levels until none remain, then simplifying away ‘.’ and ‘..’ appearing as name components. This results in a sort of canonical name for the file. A file does not always have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
The function
file-truenamereturns the truename of the file filename. The argument must be an absolute file name.This function does not expand environment variables. Only
substitute-in-file-namedoes that. See Definition of substitute-in-file-name.If you may need to follow symbolic links preceding ‘..’ appearing as a name component, you should make sure to call
file-truenamewithout prior direct or indirect calls toexpand-file-name, as otherwise the file name component immediately preceding ‘..’ will be “simplified away” beforefile-truenameis called. To eliminate the need for a call toexpand-file-name,file-truenamehandles ‘~’ in the same way thatexpand-file-namedoes. See Functions that Expand Filenames.
This function follows symbolic links, starting with filename, until it finds a file name which is not the name of a symbolic link. Then it returns that file name. This function does not follow symbolic links at the level of parent directories.
If you specify a number for limit, then after chasing through that many links, the function just returns what it has even if that is still a symbolic link.
To illustrate the difference between file-chase-links and
file-truename, suppose that /usr/foo is a symbolic link to
the directory /home/foo, and /home/foo/hello is an
ordinary file (or at least, not a symbolic link) or nonexistent. Then
we would have:
(file-chase-links "/usr/foo/hello")
;; This does not follow the links in the parent directories.
⇒ "/usr/foo/hello"
(file-truename "/usr/foo/hello")
;; Assuming that /home is not a symbolic link.
⇒ "/home/foo/hello"
See Buffer File Name, for related information.
This section describes the functions for getting detailed information about a file, other than its contents. This information includes the mode bits that control access permission, the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.
This function returns the mode bits of filename, as an integer. The mode bits are also called the file permissions, and they specify access control in the usual Unix fashion. If the low-order bit is 1, then the file is executable by all users, if the second-lowest-order bit is 1, then the file is writable by all users, etc.
The highest value returnable is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, that the SUID bit is set for both others and group, and that the sticky bit is set.
If filename does not exist,
file-modesreturnsnil.This function recursively follows symbolic links at all levels.
(file-modes "~/junk/diffs") ⇒ 492 ; Decimal integer. (format "%o" 492) ⇒ "754" ; Convert to octal. (set-file-modes "~/junk/diffs" 438) ⇒ nil (format "%o" 438) ⇒ "666" ; Convert to octal. % ls -l diffs -rw-rw-rw- 1 lewis 0 3063 Oct 30 16:00 diffs
If the filename argument to the next two functions is a symbolic link, then these function do not replace it with its target. However, they both recursively follow symbolic links at all levels of parent directories.
This functions returns the number of names (i.e., hard links) that file filename has. If the file does not exist, then this function returns
nil. Note that symbolic links have no effect on this function, because they are not considered to be names of the files they link to.% ls -l foo* -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo -rw-rw-rw- 2 rms 4 Aug 19 01:27 foo1 (file-nlinks "foo") ⇒ 2 (file-nlinks "doesnt-exist") ⇒ nil
This function returns a list of attributes of file filename. If the specified file cannot be opened, it returns
nil. The optional parameter id-format specifies the preferred format of attributes UID and GID (see below)—the valid values are'stringand'integer. The latter is the default, but we plan to change that, so you should specify a non-nilvalue for id-format if you use the returned UID or GID.The elements of the list, in order, are:
tfor a directory, a string for a symbolic link (the name linked to), ornilfor a text file.- The number of names the file has. Alternate names, also known as hard links, can be created by using the
add-name-to-filefunction (see Changing Files).- The file's UID, normally as a string. However, if it does not correspond to a named user, the value is an integer or a floating point number.
- The file's GID, likewise.
- The time of last access, as a list of two integers. The first integer has the high-order 16 bits of time, the second has the low 16 bits. (This is similar to the value of
current-time; see Time of Day.) Note that on some FAT-based filesystems, only the date of last access is recorded, so this time will always hold the midnight of the day of last access.- The time of last modification as a list of two integers (as above). This is the last time when the file's contents were modified.
- The time of last status change as a list of two integers (as above). This is the time of the last change to the file's access mode bits, its owner and group, and other information recorded in the filesystem for the file, beyond the file's contents.
- The size of the file in bytes. If the size is too large to fit in a Lisp integer, this is a floating point number.
- The file's modes, as a string of ten letters or dashes, as in ‘ls -l’.
tif the file's GID would change if file were deleted and recreated;nilotherwise.- The file's inode number. If possible, this is an integer. If the inode number is too large to be represented as an integer in Emacs Lisp, but still fits into a 32-bit integer, then the value has the form
(high.low), where low holds the low 16 bits. If the inode is wider than 32 bits, the value is of the form(high middle.low), wherehighholds the high 24 bits, middle the next 24 bits, and low the low 16 bits.- The filesystem number of the device that the file is on. Depending on the magnitude of the value, this can be either an integer or a cons cell, in the same manner as the inode number. This element and the file's inode number together give enough information to distinguish any two files on the system—no two files can have the same values for both of these numbers.
For example, here are the file attributes for files.texi:
(file-attributes "files.texi" 'string) ⇒ (nil 1 "lh" "users" (19145 42977) (19141 59576) (18340 17300) 122295 "-rw-rw-rw-" nil (5888 2 . 43978) (15479 . 46724))and here is how the result is interpreted:
nil- is neither a directory nor a symbolic link.
1- has only one name (the name files.texi in the current default directory).
"lh"- is owned by the user with name "lh".
"users"- is in the group with name "users".
(19145 42977)- was last accessed on Oct 5 2009, at 10:01:37.
(19141 59576)- last had its contents modified on Oct 2 2009, at 13:49:12.
(18340 17300)- last had its status changed on Feb 2 2008, at 12:19:00.
122295- is 122295 bytes long. (It may not contain 122295 characters, though, if some of the bytes belong to multibyte sequences, and also if the end-of-line format is CR-LF.)
"-rw-rw-rw-"- has a mode of read and write access for the owner, group, and world.
nil- would retain the same GID if it were recreated.
(5888 2 . 43978)- has an inode number of 6473924464520138.
(15479 . 46724)- is on the file-system device whose number is 1014478468.
On MS-DOS, there is no such thing as an “executable” file mode bit.
So Emacs considers a file executable if its name ends in one of the
standard executable extensions, such as .com, .bat,
.exe, and some others. Files that begin with the Unix-standard
‘#!’ signature, such as shell and Perl scripts, are also considered
as executable files. This is reflected in the values returned by
file-modes and file-attributes. Directories are also
reported with executable bit set, for compatibility with Unix.
This section explains how to search for a file in a list of directories (a path). One example is when you need to look for a program's executable file, e.g., to find out whether a given program is installed on the user's system. Another example is the search for Lisp libraries (see Library Search). Such searches generally need to try various possible file name extensions, in addition to various possible directories. Emacs provides a function for such a generalized search for a file.
This function searches for a file whose name is filename in a list of directories given by path, trying the suffixes in suffixes. If it finds such a file, it returns the full absolute file name of the file (see Relative File Names); otherwise it returns
nil.The optional argument suffixes gives the list of file-name suffixes to append to filename when searching.
locate-filetries each possible directory with each of these suffixes. If suffixes isnil, or(""), then there are no suffixes, and filename is used only as-is. Typical values of suffixes areexec-suffixes(see exec-suffixes),load-suffixes,load-file-rep-suffixesand the return value of the functionget-load-suffixes(see Load Suffixes).Typical values for path are
exec-path(see exec-path) when looking for executable programs orload-path(see load-path) when looking for Lisp files. If filename is absolute, path has no effect, but the suffixes in suffixes are still tried.The optional argument predicate, if non-
nil, specifies the predicate function to use for testing whether a candidate file is suitable. The predicate function is passed the candidate file name as its single argument. If predicate isnilor unspecified,locate-fileusesfile-readable-pas the default predicate. Useful non-default predicates includefile-executable-p,file-directory-p, and other predicates described in Kinds of Files.For compatibility, predicate can also be one of the symbols
executable,readable,writable,exists, or a list of one or more of these symbols.
This function searches for the executable file of the named program and returns the full absolute name of the executable, including its file-name extensions, if any. It returns
nilif the file is not found. The functions searches in all the directories inexec-pathand tries all the file-name extensions inexec-suffixes.
The functions in this section rename, copy, delete, link, and set the modes of files.
In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists:
file-already-exists error if
ok-if-already-exists is nil.
The next four commands all recursively follow symbolic links at all
levels of parent directories for their first argument, but, if that
argument is itself a symbolic link, then only copy-file
replaces it with its (recursive) target.
This function gives the file named oldname the additional name newname. This means that newname becomes a new “hard link” to oldname.
In the first part of the following example, we list two files, foo and foo3.
% ls -li fo* 81908 -rw-rw-rw- 1 rms 29 Aug 18 20:32 foo 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3Now we create a hard link, by calling
add-name-to-file, then list the files again. This shows two names for one file, foo and foo2.(add-name-to-file "foo" "foo2") ⇒ nil % ls -li fo* 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 2 rms 29 Aug 18 20:32 foo2 84302 -rw-rw-rw- 1 rms 24 Aug 18 20:31 foo3Finally, we evaluate the following:
(add-name-to-file "foo" "foo3" t)and list the files again. Now there are three names for one file: foo, foo2, and foo3. The old contents of foo3 are lost.
(add-name-to-file "foo1" "foo3") ⇒ nil % ls -li fo* 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo2 81908 -rw-rw-rw- 3 rms 29 Aug 18 20:32 foo3This function is meaningless on operating systems where multiple names for one file are not allowed. Some systems implement multiple names by copying the file instead.
See also
file-nlinksin File Attributes.
This command renames the file filename as newname.
If filename has additional names aside from filename, it continues to have those names. In fact, adding the name newname with
add-name-to-fileand then deleting filename has the same effect as renaming, aside from momentary intermediate states.
This command copies the file oldname to newname. An error is signaled if oldname does not exist. If newname names a directory, it copies oldname into that directory, preserving its final name component.
If time is non-
nil, then this function gives the new file the same last-modified time that the old one has. (This works on only some operating systems.) If setting the time gets an error,copy-filesignals afile-date-errorerror. In an interactive call, a prefix argument specifies a non-nilvalue for time.This function copies the file modes, too.
If argument preserve-uid-gid is
nil, we let the operating system decide the user and group ownership of the new file (this is usually set to the user running Emacs). If preserve-uid-gid is non-nil, we attempt to copy the user and group ownership of the file. This works only on some operating systems, and only if you have the correct permissions to do so.
This command makes a symbolic link to filename, named newname. This is like the shell command ‘ln -s filename newname’.
This function is not available on systems that don't support symbolic links.
This command deletes the file filename, like the shell command ‘rm filename’. If the file has multiple names, it continues to exist under the other names.
A suitable kind of
file-errorerror is signaled if the file does not exist, or is not deletable. (On Unix and GNU/Linux, a file is deletable if its directory is writable.)If filename is a symbolic link,
delete-filedoes not replace it with its target, but it does follow symbolic links at all levels of parent directories.See also
delete-directoryin Create/Delete Dirs.
This function sets mode bits of filename to mode (which must be an integer when the function is called non-interactively). Only the low 12 bits of mode are used.
Interactively, mode is read from the minibuffer using
read-file-modes, which accepts mode bits either as a number or as a character string representing the mode bits symbolically. See the description ofread-file-modesbelow for the supported forms of symbolic notation for mode bits.This function recursively follows symbolic links at all levels for filename.
This function sets the default file protection for new files created by Emacs and its subprocesses. Every file created with Emacs initially has this protection, or a subset of it (
write-regionwill not give a file execute permission even if the default file protection allows execute permission). On Unix and GNU/Linux, the default protection is the bitwise complement of the “umask” value.The argument mode must be an integer. On most systems, only the low 9 bits of mode are meaningful. You can use the Lisp construct for octal character codes to enter mode; for example,
(set-default-file-modes ?\644)Saving a modified version of an existing file does not count as creating the file; it preserves the existing file's mode, whatever that is. So the default file protection has no effect.
This function reads file mode bits from the minibuffer. The optional argument prompt specifies a non-default prompt. Second optional argument base-file is the name of a file on whose permissions to base the mode bits that this function returns, if what the user types specifies mode bits relative to permissions of an existing file.
If user input represents an octal number, this function returns that number. If it is a complete symbolic specification of mode bits, as in
"u=rwx", the function converts it to the equivalent numeric value usingfile-modes-symbolic-to-numberand returns the result. If the specification is relative, as in"o+g", then the permissions on which the specification is based are taken from the mode bits of base-file. If base-file is omitted ornil, the function uses0as the base mode bits. The complete and relative specifications can be combined, as in"u+r,g+rx,o+r,g-w". See File Permissions, for detailed description of symbolic mode bits specifications.
This subroutine converts a symbolic specification of file mode bits in modes into the equivalent numeric value. If the symbolic specification is based on an existing file, that file's mode bits are taken from the optional argument base-modes; if that argument is omitted or
nil, it defaults to zero, i.e. no access rights at all.
This function sets the access and modification times of filename to time. The return value is
tif the times are successfully set, otherwise it isnil. time defaults to the current time and must be in the format returned bycurrent-time(see Time of Day).
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs often need to operate on file names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.
On MS-DOS and MS-Windows, these functions (like the function that actually operate on files) accept MS-DOS or MS-Windows file-name syntax, where backslashes separate the components, as well as Unix syntax; but they always return Unix syntax. This enables Lisp programs to specify file names in Unix syntax and work properly on all systems without change.
The operating system groups files into directories. To specify a file, you must specify the directory and the file's name within that directory. Therefore, Emacs considers a file name as having two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.
On most systems, the directory part is everything up to and including the last slash (backslash is also allowed in input on MS-DOS or MS-Windows); the nondirectory part is the rest.
For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On most systems, only backup files have version numbers in their names.
This function returns the directory part of filename, as a directory name (see Directory Names), or
nilif filename does not include a directory part.On GNU and Unix systems, a string returned by this function always ends in a slash. On MS-DOS it can also end in a colon.
(file-name-directory "lewis/foo") ; Unix example ⇒ "lewis/" (file-name-directory "foo") ; Unix example ⇒ nil
This function returns the nondirectory part of filename.
(file-name-nondirectory "lewis/foo") ⇒ "foo" (file-name-nondirectory "foo") ⇒ "foo" (file-name-nondirectory "lewis/") ⇒ ""
This function returns filename with any file version numbers, backup version numbers, or trailing tildes discarded.
If keep-backup-version is non-
nil, then true file version numbers understood as such by the file system are discarded from the return value, but backup version numbers are kept.(file-name-sans-versions "~rms/foo.~1~") ⇒ "~rms/foo" (file-name-sans-versions "~rms/foo~") ⇒ "~rms/foo" (file-name-sans-versions "~rms/foo") ⇒ "~rms/foo"
This function returns filename's final “extension,” if any, after applying
file-name-sans-versionsto remove any version/backup part. The extension, in a file name, is the part that follows the last ‘.’ in the last name component (minus any version/backup part).This function returns
nilfor extensionless file names such as foo. It returns""for null extensions, as in foo.. If the last component of a file name begins with a ‘.’, that ‘.’ doesn't count as the beginning of an extension. Thus, .emacs's “extension” isnil, not ‘.emacs’.If period is non-
nil, then the returned value includes the period that delimits the extension, and if filename has no extension, the value is"".
This function returns filename minus its extension, if any. The version/backup part, if present, is only removed if the file has an extension. For example,
(file-name-sans-extension "foo.lose.c") ⇒ "foo.lose" (file-name-sans-extension "big.hack/foo") ⇒ "big.hack/foo" (file-name-sans-extension "/my/home/.emacs") ⇒ "/my/home/.emacs" (file-name-sans-extension "/my/home/.emacs.el") ⇒ "/my/home/.emacs" (file-name-sans-extension "~/foo.el.~3~") ⇒ "~/foo" (file-name-sans-extension "~/foo.~3~") ⇒ "~/foo.~3~"Note that the ‘.~3~’ in the two last examples is the backup part, not an extension.
All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a relative file name. On Unix and GNU/Linux, an absolute file name starts with a slash or a tilde (‘~’), and a relative one does not. On MS-DOS and MS-Windows, an absolute file name starts with a slash or a backslash, or with a drive specification ‘x:/’, where x is the drive letter.
This function returns
tif file filename is an absolute file name,nilotherwise.(file-name-absolute-p "~rms/foo") ⇒ t (file-name-absolute-p "rms/foo") ⇒ nil (file-name-absolute-p "/user/rms/foo") ⇒ t
Given a possibly relative file name, you can convert it to an
absolute name using expand-file-name (see File Name Expansion). This function converts absolute file names to relative
names:
This function tries to return a relative name that is equivalent to filename, assuming the result will be interpreted relative to directory (an absolute directory name or directory file name). If directory is omitted or
nil, it defaults to the current buffer's default directory.On some operating systems, an absolute file name begins with a device name. On such systems, filename has no relative equivalent based on directory if they start with two different device names. In this case,
file-relative-namereturns filename in absolute form.(file-relative-name "/foo/bar" "/foo/") ⇒ "bar" (file-relative-name "/foo/bar" "/hack/") ⇒ "../foo/bar"
A directory name is the name of a directory. A directory is actually a kind of file, so it has a file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On GNU and Unix systems, this is simple: a directory name ends in a slash, whereas the directory's name as a file lacks that slash. On MS-DOS the relationship is more complicated.
The difference between a directory name and its name as a file is
subtle but crucial. When an Emacs variable or function argument is
described as being a directory name, a file name of a directory is not
acceptable. When file-name-directory returns a string, that is
always a directory name.
The following two functions convert between directory names and file names. They do nothing special with environment variable substitutions such as ‘$HOME’, and the constructs ‘~’, ‘.’ and ‘..’.
This function returns a string representing filename in a form that the operating system will interpret as the name of a directory. On most systems, this means appending a slash to the string (if it does not already end in one).
(file-name-as-directory "~rms/lewis") ⇒ "~rms/lewis/"
This function returns a string representing dirname in a form that the operating system will interpret as the name of a file. On most systems, this means removing the final slash (or backslash) from the string.
(directory-file-name "~lewis/") ⇒ "~lewis"
Given a directory name, you can combine it with a relative file name
using concat:
(concat dirname relfile)
Be sure to verify that the file name is relative before doing that. If you use an absolute file name, the results could be syntactically invalid or refer to the wrong file.
If you want to use a directory file name in making such a
combination, you must first convert it to a directory name using
file-name-as-directory:
(concat (file-name-as-directory dirfile) relfile)
Don't try concatenating a slash by hand, as in
;;; Wrong!
(concat dirfile "/" relfile)
because this is not portable. Always use
file-name-as-directory.
To convert a directory name to its abbreviation, use this function:
This function returns an abbreviated form of filename. It applies the abbreviations specified in
directory-abbrev-alist(see File Aliases), then substitutes ‘~’ for the user's home directory if the argument names a file in the home directory or one of its subdirectories. If the home directory is a root directory, it is not replaced with ‘~’, because this does not make the result shorter on many systems.You can use this function for directory names and for file names, because it recognizes abbreviations even as part of the name.
Expansion of a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. Expansion also simplifies file names by eliminating redundancies such as ./ and name/../.
This function converts filename to an absolute file name. If directory is supplied, it is the default directory to start with if filename is relative. (The value of directory should itself be an absolute directory name or directory file name; it may start with ‘~’.) Otherwise, the current buffer's value of
default-directoryis used. For example:(expand-file-name "foo") ⇒ "/xcssun/users/rms/lewis/foo" (expand-file-name "../foo") ⇒ "/xcssun/users/rms/foo" (expand-file-name "foo" "/usr/spool/") ⇒ "/usr/spool/foo" (expand-file-name "$HOME/foo") ⇒ "/xcssun/users/rms/lewis/$HOME/foo"If the part of the combined file name before the first slash is ‘~’, it expands to the value of the HOME environment variable (usually your home directory). If the part before the first slash is ‘~user’ and if user is a valid login name, it expands to user's home directory.
Filenames containing ‘.’ or ‘..’ are simplified to their canonical form:
(expand-file-name "bar/../foo") ⇒ "/xcssun/users/rms/lewis/foo"In some cases, a leading ‘..’ component can remain in the output:
(expand-file-name "../home" "/") ⇒ "/../home"This is for the sake of filesystems that have the concept of a “superroot” above the root directory /. On other filesystems, /../ is interpreted exactly the same as /.
Note that
expand-file-namedoes not expand environment variables; onlysubstitute-in-file-namedoes that.Note also that
expand-file-namedoes not follow symbolic links at any level. This results in a difference between the wayfile-truenameandexpand-file-nametreat ‘..’. Assuming that ‘/tmp/bar’ is a symbolic link to the directory ‘/tmp/foo/bar’ we get:(file-truename "/tmp/bar/../myfile") ⇒ "/tmp/foo/myfile" (expand-file-name "/tmp/bar/../myfile") ⇒ "/tmp/myfile"If you may need to follow symbolic links preceding ‘..’, you should make sure to call
file-truenamewithout prior direct or indirect calls toexpand-file-name. See Truenames.
The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with ‘~’. This variable is buffer-local in every buffer.
expand-file-nameuses the default directory when its second argument isnil.The value is always a string ending with a slash.
default-directory ⇒ "/user/lewis/manual/"
This function replaces environment variable references in filename with the environment variable values. Following standard Unix shell syntax, ‘$’ is the prefix to substitute an environment variable value. If the input contains ‘$$’, that is converted to ‘$’; this gives the user a way to “quote” a ‘$’.
The environment variable name is the series of alphanumeric characters (including underscores) that follow the ‘$’. If the character following the ‘$’ is a ‘{’, then the variable name is everything up to the matching ‘}’.
Calling
substitute-in-file-nameon output produced bysubstitute-in-file-nametends to give incorrect results. For instance, use of ‘$$’ to quote a single ‘$’ won't work properly, and ‘$’ in an environment variable's value could lead to repeated substitution. Therefore, programs that call this function and put the output where it will be passed to this function need to double all ‘$’ characters to prevent subsequent incorrect results.Here we assume that the environment variable
HOME, which holds the user's home directory name, has value ‘/xcssun/users/rms’.(substitute-in-file-name "$HOME/foo") ⇒ "/xcssun/users/rms/foo"After substitution, if a ‘~’ or a ‘/’ appears immediately after another ‘/’, the function discards everything before it (up through the immediately preceding ‘/’).
(substitute-in-file-name "bar/~/foo") ⇒ "~/foo" (substitute-in-file-name "/usr/local/$HOME/foo") ⇒ "/xcssun/users/rms/foo" ;; /usr/local/ has been discarded.
Some programs need to write temporary files. Here is the usual way to construct a name for such a file:
(make-temp-file name-of-application)
The job of make-temp-file is to prevent two different users or
two different jobs from trying to use the exact same file name.
This function creates a temporary file and returns its name. Emacs creates the temporary file's name by adding to prefix some random characters that are different in each Emacs job. The result is guaranteed to be a newly created empty file. On MS-DOS, this function can truncate the string prefix to fit into the 8+3 file-name limits. If prefix is a relative file name, it is expanded against
temporary-file-directory.(make-temp-file "foo") ⇒ "/tmp/foo232J6v"When
make-temp-filereturns, the file has been created and is empty. At that point, you should write the intended contents into the file.If dir-flag is non-
nil,make-temp-filecreates an empty directory instead of an empty file. It returns the file name, not the directory name, of that directory. See Directory Names.If suffix is non-
nil,make-temp-fileadds it at the end of the file name.To prevent conflicts among different libraries running in the same Emacs, each Lisp program that uses
make-temp-fileshould have its own prefix. The number added to the end of prefix distinguishes between the same application running in different Emacs jobs. Additional added characters permit a large number of distinct names even in one Emacs job.
The default directory for temporary files is controlled by the
variable temporary-file-directory. This variable gives the user
a uniform way to specify the directory for all temporary files. Some
programs use small-temporary-file-directory instead, if that is
non-nil. To use it, you should expand the prefix against
the proper directory before calling make-temp-file.
In older Emacs versions where make-temp-file does not exist,
you should use make-temp-name instead:
(make-temp-name
(expand-file-name name-of-application
temporary-file-directory))
This function generates a string that can be used as a unique file name. The name starts with string, and has several random characters appended to it, which are different in each Emacs job. It is like
make-temp-fileexcept that it just constructs a name, and does not create a file. Another difference is that string should be an absolute file name. On MS-DOS, this function can truncate the string prefix to fit into the 8+3 file-name limits.
This variable specifies the directory name for creating temporary files. Its value should be a directory name (see Directory Names), but it is good for Lisp programs to cope if the value is a directory's file name instead. Using the value as the second argument to
expand-file-nameis a good way to achieve that.The default value is determined in a reasonable way for your operating system; it is based on the
TMPDIR,TMPandTEMPenvironment variables, with a fall-back to a system-dependent name if none of these variables is defined.Even if you do not use
make-temp-fileto create the temporary file, you should still use this variable to decide which directory to put the file in. However, if you expect the file to be small, you should usesmall-temporary-file-directoryfirst if that is non-nil.
This variable specifies the directory name for creating certain temporary files, which are likely to be small.
If you want to write a temporary file which is likely to be small, you should compute the directory like this:
(make-temp-file (expand-file-name prefix (or small-temporary-file-directory temporary-file-directory)))
This section describes low-level subroutines for completing a file name. For higher level functions, see Reading File Names.
This function returns a list of all possible completions for a file whose name starts with partial-filename in directory directory. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information.
The argument partial-filename must be a file name containing no directory part and no slash (or backslash on some systems). The current buffer's default directory is prepended to directory, if directory is not absolute.
In the following example, suppose that ~rms/lewis is the current default directory, and has five files whose names begin with ‘f’: foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-all-completions "f" "") ⇒ ("foo" "file~" "file.c.~2~" "file.c.~1~" "file.c") (file-name-all-completions "fo" "") ⇒ ("foo")
This function completes the file name filename in directory directory. It returns the longest prefix common to all file names in directory directory that start with filename. If predicate is non-
nilthen it ignores possible completions that don't satisfy predicate, after calling that function with one argument, the expanded absolute file name.If only one match exists and filename matches it exactly, the function returns
t. The function returnsnilif directory directory contains no name starting with filename.In the following example, suppose that the current default directory has five files whose names begin with ‘f’: foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-completion "fi" "") ⇒ "file" (file-name-completion "file.c.~1" "") ⇒ "file.c.~1~" (file-name-completion "file.c.~1~" "") ⇒ t (file-name-completion "file.c.~3" "") ⇒ nil
file-name-completionusually ignores file names that end in any string in this list. It does not ignore them when all the possible completions end in one of these suffixes. This variable has no effect onfile-name-all-completions.A typical value might look like this:
completion-ignored-extensions ⇒ (".o" ".elc" "~" ".dvi")If an element of
completion-ignored-extensionsends in a slash ‘/’, it signals a directory. The elements which do not end in a slash will never match a directory; thus, the above value will not filter out a directory named foo.elc.
Most of the file names used in Lisp programs are entered by the user.
But occasionally a Lisp program needs to specify a standard file name
for a particular use—typically, to hold customization information
about each user. For example, abbrev definitions are stored (by
default) in the file ~/.abbrev_defs; the completion
package stores completions in the file ~/.completions. These are
two of the many standard file names used by parts of Emacs for certain
purposes.
Various operating systems have their own conventions for valid file
names and for which file names to use for user profile data. A Lisp
program which reads a file using a standard file name ought to use, on
each type of system, a file name suitable for that system. The function
convert-standard-filename makes this easy to do.
This function alters the file name filename to fit the conventions of the operating system in use, and returns the result as a new string.
The recommended way to specify a standard file name in a Lisp program
is to choose a name which fits the conventions of GNU and Unix systems,
usually with a nondirectory part that starts with a period, and pass it
to convert-standard-filename instead of using it directly. Here
is an example from the completion package:
(defvar save-completions-file-name
(convert-standard-filename "~/.completions")
"*The file name to save completions to.")
On GNU and Unix systems, and on some other systems as well,
convert-standard-filename returns its argument unchanged. On
some other systems, it alters the name to fit the system's conventions.
For example, on MS-DOS the alterations made by this function include converting a leading ‘.’ to ‘_’, converting a ‘_’ in the middle of the name to ‘.’ if there is no other ‘.’, inserting a ‘.’ after eight characters if there is none, and truncating to three characters after the ‘.’. (It makes other changes as well.) Thus, .abbrev_defs becomes _abbrev.def, and .completions becomes _complet.ion.
A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the ls shell command. In
the latter case, it can optionally display information about each file,
depending on the options passed to the ls command.
This function returns a list of the names of the files in the directory directory. By default, the list is in alphabetical order.
If full-name is non-
nil, the function returns the files' absolute file names. Otherwise, it returns the names relative to the specified directory.If match-regexp is non-
nil, this function returns only those file names that contain a match for that regular expression—the other file names are excluded from the list. On case-insensitive filesystems, the regular expression matching is case-insensitive.If nosort is non-
nil,directory-filesdoes not sort the list, so you get the file names in no particular order. Use this if you want the utmost possible speed and don't care what order the files are processed in. If the order of processing is visible to the user, then the user will probably be happier if you do sort the names.(directory-files "~lewis") ⇒ ("#foo#" "#foo.el#" "." ".." "dired-mods.el" "files.texi" "files.texi.~1~")An error is signaled if directory is not the name of a directory that can be read.
This is similar to
directory-filesin deciding which files to report on and how to report their names. However, instead of returning a list of file names, it returns for each file a list(filename.attributes), where attributes is whatfile-attributeswould return for that file. The optional argument id-format has the same meaning as the corresponding argument tofile-attributes(see Definition of file-attributes).
This function expands the wildcard pattern pattern, returning a list of file names that match it.
If pattern is written as an absolute file name, the values are absolute also.
If pattern is written as a relative file name, it is interpreted relative to the current default directory. The file names returned are normally also relative to the current default directory. However, if full is non-
nil, they are absolute.
This function inserts (in the current buffer) a directory listing for directory file, formatted with
lsaccording to switches. It leaves point after the inserted text. switches may be a string of options, or a list of strings representing individual options.The argument file may be either a directory name or a file specification including wildcard characters. If wildcard is non-
nil, that means treat file as a file specification with wildcards.If full-directory-p is non-
nil, that means the directory listing is expected to show the full contents of a directory. You should specifytwhen file is a directory and switches do not contain ‘-d’. (The ‘-d’ option tolssays to describe a directory itself as a file, rather than showing its contents.)On most systems, this function works by running a directory listing program whose name is in the variable
insert-directory-program. If wildcard is non-nil, it also runs the shell specified byshell-file-name, to expand the wildcards.MS-DOS and MS-Windows systems usually lack the standard Unix program
ls, so this function emulates the standard Unix programlswith Lisp code.As a technical detail, when switches contains the long ‘--dired’ option,
insert-directorytreats it specially, for the sake of dired. However, the normally equivalent short ‘-D’ option is just passed on toinsert-directory-program, as any other option.
This variable's value is the program to run to generate a directory listing for the function
insert-directory. It is ignored on systems which generate the listing with Lisp code.
Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories. For example, you cannot delete a directory
with delete-file. These special functions exist to create and
delete directories.
This command creates a directory named dirname. If parents is non-
nil, as is always the case in an interactive call, that means to create the parent directories first, if they don't already exist.
mkdiris an alias for this.
This command copies the directory named dirname to newname. If newname names an existing directory, dirname will be copied to a subdirectory there.
It always sets the file modes of the copied files to match the corresponding original file.
The third arg keep-time non-
nilmeans to preserve the modification time of the copied files. A prefix arg makes keep-time non-nil.Noninteractively, the last argument parents says whether to create parent directories if they don't exist. Interactively, this happens by default.
This command deletes the directory named dirname. The function
delete-filedoes not work for files that are directories; you must usedelete-directoryfor them. If recursive isnil, and the directory contains any files,delete-directorysignals an error.
delete-directoryonly follows symbolic links at the level of parent directories.
You can implement special handling for certain file names. This is called making those names magic. The principal use for this feature is in implementing remote file names (see Remote Files).
To define a kind of magic file name, you must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that do match.
The variable file-name-handler-alist holds a list of handlers,
together with regular expressions that determine when to apply each
handler. Each element has this form:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to handler is the name of the primitive, as a symbol; the remaining arguments are the arguments that were passed to that primitive. (The first of these arguments is most often the file name itself.) For example, if you do this:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
When a function takes two or more arguments that must be file names, it checks each of those names for a handler. For example, if you do this:
(expand-file-name filename dirname)
then it checks for a handler for filename and then for a handler for dirname. In either case, the handler is called like this:
(funcall handler 'expand-file-name filename dirname)
The handler then needs to figure out whether to handle filename or dirname.
If the specified file name matches more than one handler, the one whose match starts last in the file name gets precedence. This rule is chosen so that handlers for jobs such as uncompression are handled first, before handlers for jobs such as remote file access.
Here are the operations that a magic file name handler gets to handle:
access-file, add-name-to-file,
byte-compiler-base-file-name,
copy-directory, copy-file,
delete-directory, delete-file,
diff-latest-backup-file,
directory-file-name,
directory-files,
directory-files-and-attributes,
dired-compress-file, dired-uncache,
expand-file-name,
file-accessible-directory-p,
file-attributes,
file-directory-p,
file-executable-p, file-exists-p,
file-local-copy, file-remote-p,
file-modes, file-name-all-completions,
file-name-as-directory,
file-name-completion,
file-name-directory,
file-name-nondirectory,
file-name-sans-versions, file-newer-than-file-p,
file-ownership-preserved-p,
file-readable-p, file-regular-p, file-symlink-p,
file-truename, file-writable-p,
find-backup-file-name,
get-file-buffer,
insert-directory,
insert-file-contents,
load,
make-auto-save-file-name,
make-directory,
make-directory-internal,
make-symbolic-link,
process-file,
rename-file, set-file-modes, set-file-times,
set-visited-file-modtime, shell-command,
start-file-process,
substitute-in-file-name,
unhandled-file-name-directory,
vc-registered,
verify-visited-file-modtime,
write-region.
Handlers for insert-file-contents typically need to clear the
buffer's modified flag, with (set-buffer-modified-p nil), if the
visit argument is non-nil. This also has the effect of
unlocking the buffer if it is locked.
The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself—when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation “in the usual way.” It should always reinvoke the primitive for an operation it does not recognize. Here's one way to do this:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let ((inhibit-file-name-handlers
(cons 'my-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))))
When a handler function decides to call the ordinary Emacs primitive for
the operation at hand, it needs to prevent the primitive from calling
the same handler once again, thus leading to an infinite recursion. The
example above shows how to do this, with the variables
inhibit-file-name-handlers and
inhibit-file-name-operation. Be careful to use them exactly as
shown above; the details are crucial for proper behavior in the case of
multiple handlers, and for operations that have two file names that may
each have handlers.
Handlers that don't really do anything special for actual access to the
file—such as the ones that implement completion of host names for
remote file names—should have a non-nil safe-magic
property. For instance, Emacs normally “protects” directory names
it finds in PATH from becoming magic, if they look like magic
file names, by prefixing them with ‘/:’. But if the handler that
would be used for them has a non-nil safe-magic
property, the ‘/:’ is not added.
A file name handler can have an operations property to
declare which operations it handles in a nontrivial way. If this
property has a non-nil value, it should be a list of
operations; then only those operations will call the handler. This
avoids inefficiency, but its main purpose is for autoloaded handler
functions, so that they won't be loaded except when they have real
work to do.
Simply deferring all operations to the usual primitives does not
work. For instance, if the file name handler applies to
file-exists-p, then it must handle load itself, because
the usual load code won't work properly in that case. However,
if the handler uses the operations property to say it doesn't
handle file-exists-p, then it need not handle load
nontrivially.
This variable holds a list of handlers whose use is presently inhibited for a certain operation.
The operation for which certain handlers are presently inhibited.
This function returns the handler function for file name file, or
nilif there is none. The argument operation should be the operation to be performed on the file—the value you will pass to the handler as its first argument when you call it. If operation equalsinhibit-file-name-operation, or if it is not found in theoperationsproperty of the handler, this function returnsnil.
This function copies file filename to an ordinary non-magic file on the local machine, if it isn't on the local machine already. Magic file names should handle the
file-local-copyoperation if they refer to files on other machines. A magic file name that is used for other purposes than remote file access should not handlefile-local-copy; then this function will treat the file as local.If filename is local, whether magic or not, this function does nothing and returns
nil. Otherwise it returns the file name of the local copy file.
This function tests whether filename is a remote file. If filename is local (not remote), the return value is
nil. If filename is indeed remote, the return value is a string that identifies the remote system.This identifier string can include a host name and a user name, as well as characters designating the method used to access the remote system. For example, the remote identifier string for the filename
/sudo::/some/fileis/sudo:root@localhost:.If
file-remote-preturns the same identifier for two different filenames, that means they are stored on the same file system and can be accessed locally with respect to each other. This means, for example, that it is possible to start a remote process accessing both files at the same time. Implementors of file handlers need to ensure this principle is valid.identification specifies which part of the identifier shall be returned as string. identification can be the symbol
method,userorhost; any other value is handled likeniland means to return the complete identifier string. In the example above, the remoteuseridentifier string would beroot.If connected is non-
nil, this function returnsnileven if filename is remote, if Emacs has no network connection to its host. This is useful when you want to avoid the delay of making connections when they don't exist.
This function returns the name of a directory that is not magic. It uses the directory part of filename if that is not magic. For a magic file name, it invokes the file name handler, which therefore decides what value to return. If filename is not accessible from a local process, then the file name handler should indicate it by returning
nil.This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.
Emacs performs several steps to convert the data in a buffer (text,
text properties, and possibly other information) to and from a
representation suitable for storing into a file. This section describes
the fundamental functions that perform this format conversion,
namely insert-file-contents for reading a file into a buffer,
and write-region for writing a buffer into a file.
The function insert-file-contents:
format-alist; and
after-insert-file-functions.
The function write-region:
write-region-annotate-functions;
format-alist;
This shows the symmetry of the lowest-level operations; reading and writing handle things in opposite order. The rest of this section describes the two facilities surrounding the three variables named above, as well as some related functions. Coding Systems, for details on character encoding and decoding.
The most general of the two facilities is controlled by the variable
format-alist, a list of file format specifications, which
describe textual representations used in files for the data in an Emacs
buffer. The descriptions for reading and writing are paired, which is
why we call this “round-trip” specification
(see Format Conversion Piecemeal, for non-paired specification).
This list contains one format definition for each defined file format. Each format definition is a list of this form:
(name doc-string regexp from-fn to-fn modify mode-fn preserve)
Here is what the elements in a format definition mean:
nil, the format is never applied automatically.
A shell command is represented as a string; Emacs runs the command as a filter to perform the conversion.
If from-fn is a function, it is called with two arguments, begin and end, which specify the part of the buffer it should convert. It should convert the text by editing it in place. Since this can change the length of the text, from-fn should return the modified end position.
One responsibility of from-fn is to make sure that the beginning
of the file no longer matches regexp. Otherwise it is likely to
get called again.
If to-fn is a string, it is a shell command; Emacs runs the command as a filter to perform the conversion.
If to-fn is a function, it is called with three arguments: begin and end, which specify the part of the buffer it should convert, and buffer, which specifies which buffer. There are two ways it can do the conversion:
(position . string), where position is an
integer specifying the relative position in the text to be written, and
string is the annotation to add there. The list must be sorted in
order of position when to-fn returns it.
When write-region actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
t if the encoding function modifies the buffer, and
nil if it works by returning a list of annotations.
t if format-write-file should not remove this format
from buffer-file-format.
The function insert-file-contents automatically recognizes file
formats when it reads the specified file. It checks the text of the
beginning of the file against the regular expressions of the format
definitions, and if it finds a match, it calls the decoding function for
that format. Then it checks all the known formats over again.
It keeps checking them until none of them is applicable.
Visiting a file, with find-file-noselect or the commands that use
it, performs conversion likewise (because it calls
insert-file-contents); it also calls the mode function for each
format that it decodes. It stores a list of the format names in the
buffer-local variable buffer-file-format.
This variable states the format of the visited file. More precisely, this is a list of the file format names that were decoded in the course of visiting the current buffer's file. It is always buffer-local in all buffers.
When write-region writes data into a file, it first calls the
encoding functions for the formats listed in buffer-file-format,
in the order of appearance in the list.
This command writes the current buffer contents into the file file in a format based on format, which is a list of format names. It constructs the actual format starting from format, then appending any elements from the value of
buffer-file-formatwith a non-nil preserve flag (see above), if they are not already present in format. It then updatesbuffer-file-formatwith this format, making it the default for future saves. Except for the format argument, this command is similar towrite-file. In particular, confirm has the same meaning and interactive treatment as the corresponding argument towrite-file. See Definition of write-file.
This command finds the file file, converting it according to format format. It also makes format the default if the buffer is saved later.
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just <RET> for format specifiesnil.
This command inserts the contents of file file, converting it according to format format. If beg and end are non-
nil, they specify which part of the file to read, as ininsert-file-contents(see Reading from Files).The return value is like what
insert-file-contentsreturns: a list of the absolute file name and the length of the data inserted (after conversion).The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just <RET> for format specifiesnil.
This variable specifies the format to use for auto-saving. Its value is a list of format names, just like the value of
buffer-file-format; however, it is used instead ofbuffer-file-formatfor writing auto-save files. If the value ist, the default, auto-saving uses the same format as a regular save in the same buffer. This variable is always buffer-local in all buffers.
In contrast to the round-trip specification described in the previous
subsection (see Format Conversion Round-Trip), you can use the variables
after-insert-file-functions and write-region-annotate-functions
to separately control the respective reading and writing conversions.
Conversion starts with one representation and produces another representation. When there is only one conversion to do, there is no conflict about what to start with. However, when there are multiple conversions involved, conflict may arise when two conversions need to start with the same data.
This situation is best understood in the context of converting text
properties during write-region. For example, the character at
position 42 in a buffer is ‘X’ with a text property foo. If
the conversion for foo is done by inserting into the buffer, say,
‘FOO:’, then that changes the character at position 42 from
‘X’ to ‘F’. The next conversion will start with the wrong
data straight away.
To avoid conflict, cooperative conversions do not modify the buffer,
but instead specify annotations, a list of elements of the form
(position . string), sorted in order of increasing
position.
If there is more than one conversion, write-region merges their
annotations destructively into one sorted list. Later, when the text
from the buffer is actually written to the file, it intermixes the
specified annotations at the corresponding positions. All this takes
place without modifying the buffer.
In contrast, when reading, the annotations intermixed with the text
are handled immediately. insert-file-contents sets point to
the beginning of some text to be converted, then calls the conversion
functions with the length of that text. These functions should always
return with point at the beginning of the inserted text. This
approach makes sense for reading because annotations removed by the
first converter can't be mistakenly processed by a later converter.
Each conversion function should scan for the annotations it
recognizes, remove the annotation, modify the buffer text (to set a
text property, for example), and return the updated length of the
text, as it stands after those changes. The value returned by one
function becomes the argument to the next function.
A list of functions for
write-regionto call. Each function in the list is called with two arguments: the start and end of the region to be written. These functions should not alter the contents of the buffer. Instead, they should return annotations.As a special case, a function may return with a different buffer current. Emacs takes this to mean that the current buffer contains altered text to be output. It therefore changes the start and end arguments of the
write-regioncall, giving them the values ofpoint-minandpoint-maxin the new buffer, respectively. It also discards all previous annotations, because they should have been dealt with by this function.
The value of this variable, if non-
nil, should be a function. This function is called, with no arguments, afterwrite-regionhas completed.If any function in
write-region-annotate-functionsreturns with a different buffer current, Emacs callswrite-region-post-annotation-functionmore than once. Emacs calls it with the last buffer that was current, and again with the buffer before that, and so on back to the original buffer.Thus, a function in
write-region-annotate-functionscan create a buffer, give this variable the local value ofkill-bufferin that buffer, set up the buffer with altered text, and make the buffer current. The buffer will be killed afterwrite-regionis done.
Each function in this list is called by
insert-file-contentswith one argument, the number of characters inserted, and with point at the beginning of the inserted text. Each function should leave point unchanged, and return the new character count describing the inserted text as modified by the function.
We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text property names or values—because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode.
Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user's own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session.
A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Thus, normally, the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists.
Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don't want them any more, or Emacs can delete them automatically.
This function makes a backup of the file visited by the current buffer, if appropriate. It is called by
save-bufferbefore saving the buffer the first time.If a backup was made by renaming, the return value is a cons cell of the form (modes . backupname), where modes are the mode bits of the original file, as returned by
file-modes(see Other Information about Files), and backupname is the name of the backup. In all other cases, that is, if a backup was made by copying or if no backup was made, this function returnsnil.
This buffer-local variable says whether this buffer's file has been backed up on account of this buffer. If it is non-
nil, the backup file has been written. Otherwise, the file should be backed up when it is next saved (if backups are enabled). This is a permanent local;kill-all-local-variablesdoes not alter it.
This variable determines whether or not to make backup files. If it is non-
nil, then Emacs creates a backup of each file when it is saved for the first time—provided thatbackup-inhibitedisnil(see below).The following example shows how to change the
make-backup-filesvariable only in the Rmail buffers and not elsewhere. Setting itnilstops Emacs from making backups of these files, which may save disk space. (You would put this code in your init file.)(add-hook 'rmail-mode-hook (lambda () (set (make-local-variable 'make-backup-files) nil)))
This variable's value is a function to be called on certain occasions to decide whether a file should have backup files. The function receives one argument, an absolute file name to consider. If the function returns
nil, backups are disabled for that file. Otherwise, the other variables in this section say whether and how to make backups.The default value is
normal-backup-enable-predicate, which checks for files intemporary-file-directoryandsmall-temporary-file-directory.
If this variable is non-
nil, backups are inhibited. It records the result of testingbackup-enable-predicateon the visited file name. It can also coherently be used by other mechanisms that inhibit backups based on which file is visited. For example, VC sets this variable non-nilto prevent making backups for files managed with a version control system.This is a permanent local, so that changing the major mode does not lose its value. Major modes should not set this variable—they should set
make-backup-filesinstead.
This variable's value is an alist of filename patterns and backup directory names. Each element looks like
(regexp . directory)Backups of files with names matching regexp will be made in directory. directory may be relative or absolute. If it is absolute, so that all matching files are backed up into the same directory, the file names in this directory will be the full name of the file backed up with all directory separators changed to ‘!’ to prevent clashes. This will not work correctly if your filesystem truncates the resulting name.
For the common case of all backups going into one directory, the alist should contain a single element pairing ‘"."’ with the appropriate directory name.
If this variable is
nil, or it fails to match a filename, the backup is made in the original file's directory.On MS-DOS filesystems without long names this variable is always ignored.
This variable's value is a function to use for making backups instead of the default
make-backup-file-name. A value ofnilgives the defaultmake-backup-file-namebehavior. See Naming Backup Files.This could be buffer-local to do something special for specific files. If you define it, you may need to change
backup-file-name-pandfile-name-sans-versionstoo.
There are two ways that Emacs can make a backup file:
The first method, renaming, is the default.
The variable backup-by-copying, if non-nil, says to use
the second method, which is to copy the original file and overwrite it
with the new buffer contents. The variable file-precious-flag,
if non-nil, also has this effect (as a sideline of its main
significance). See Saving Buffers.
If this variable is non-
nil, Emacs always makes backup files by copying.
The following three variables, when non-nil, cause the second
method to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
If this variable is non-
nil, Emacs makes backups by copying for files with multiple names (hard links).This variable is significant only if
backup-by-copyingisnil, since copying is always used when that variable is non-nil.
If this variable is non-
nil, Emacs makes backups by copying in cases where renaming would change either the owner or the group of the file.The value has no effect when renaming would not alter the owner or group of the file; that is, for files which are owned by the user and whose group matches the default for a new file created there by the user.
This variable is significant only if
backup-by-copyingisnil, since copying is always used when that variable is non-nil.
This variable, if non-
nil, specifies the same behavior asbackup-by-copying-when-mismatch, but only for certain user-id values: namely, those less than or equal to a certain number. You set this variable to that number.Thus, if you set
backup-by-copying-when-privileged-mismatchto 0, backup by copying is done for the superuser only, when necessary to prevent a change in the owner of the file.The default is 200.
If a file's name is foo, the names of its numbered backup versions are foo.~v~, for various integers v, like this: foo.~1~, foo.~2~, foo.~3~, ..., foo.~259~, and so on.
This variable controls whether to make a single non-numbered backup file or multiple numbered backups.
nil- Make numbered backups if the visited file already has numbered backups; otherwise, do not. This is the default.
never- Do not make numbered backups.
- anything else
- Make numbered backups.
The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them.
The value of this variable is the number of newest versions to keep when a new numbered backup is made. The newly made backup is included in the count. The default value is 2.
The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess. The function find-backup-file-name
(see Backup Names) is responsible for determining which backup
versions to delete, but does not delete them itself.
If this variable is
t, then saving a file deletes excess backup versions silently. If it isnil, that means to ask for confirmation before deleting excess backups. Otherwise, they are not deleted at all.
This variable specifies how many of the newest backup versions to keep in the Dired command . (
dired-clean-directory). That's the same thingkept-new-versionsspecifies when you make a new backup file. The default is 2.
The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.
This function returns a non-
nilvalue if filename is a possible name for a backup file. It just checks the name, not whether a file with the name filename exists.(backup-file-name-p "foo") ⇒ nil (backup-file-name-p "foo~") ⇒ 3The standard definition of this function is as follows:
(defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~\\'" file))Thus, the function returns a non-
nilvalue if the file name ends with a ‘~’. (We use a backslash to split the documentation string's first line into two lines in the text, but produce just one line in the string itself.)This simple expression is placed in a separate function to make it easy to redefine for customization.
This function returns a string that is the name to use for a non-numbered backup file for file filename. On Unix, this is just filename with a tilde appended.
The standard definition of this function, on most operating systems, is as follows:
(defun make-backup-file-name (file) "Create the non-numeric backup file name for FILE..." (concat file "~"))You can change the backup-file naming convention by redefining this function. The following example redefines
make-backup-file-nameto prepend a ‘.’ in addition to appending a tilde:(defun make-backup-file-name (filename) (expand-file-name (concat "." (file-name-nondirectory filename) "~") (file-name-directory filename))) (make-backup-file-name "backups.texi") ⇒ ".backups.texi~"Some parts of Emacs, including some Dired commands, assume that backup file names end with ‘~’. If you do not follow that convention, it will not cause serious problems, but these commands may give less-than-desirable results.
This function computes the file name for a new backup file for filename. It may also propose certain existing backup files for deletion.
find-backup-file-namereturns a list whose car is the name for the new backup file and whose cdr is a list of backup files whose deletion is proposed. The value can also benil, which means not to make a backup.Two variables,
kept-old-versionsandkept-new-versions, determine which backup versions should be kept. This function keeps those versions by excluding them from the cdr of the value. See Numbered Backups.In this example, the value says that ~rms/foo.~5~ is the name to use for the new backup file, and ~rms/foo.~3~ is an “excess” version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo") ⇒ ("~rms/foo.~5~" "~rms/foo.~3~")
This function returns the name of the most recent backup file for filename, or
nilif that file has no backup files.Some file comparison commands use this function so that they can automatically compare a file with its most recent backup.
Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See Auto Save, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them.
This buffer-local variable is the name of the file used for auto-saving the current buffer. It is
nilif the buffer should not be auto-saved.buffer-auto-save-file-name ⇒ "/xcssun/users/rms/lewis/#backups.texi#"
When used interactively without an argument, this command is a toggle switch: it turns on auto-saving of the current buffer if it is off, and vice versa. With an argument arg, the command turns auto-saving on if the value of arg is
t, a nonempty list, or a positive integer. Otherwise, it turns auto-saving off.
This function returns a non-
nilvalue if filename is a string that could be the name of an auto-save file. It assumes the usual naming convention for auto-save files: a name that begins and ends with hash marks (‘#’) is a possible auto-save file name. The argument filename should not contain a directory part.(make-auto-save-file-name) ⇒ "/xcssun/users/rms/lewis/#backups.texi#" (auto-save-file-name-p "#backups.texi#") ⇒ 0 (auto-save-file-name-p "backups.texi") ⇒ nilThe standard definition of this function is as follows:
(defun auto-save-file-name-p (filename) "Return non-nil if FILENAME can be yielded by..." (string-match "^#.*#$" filename))This function exists so that you can customize it if you wish to change the naming convention for auto-save files. If you redefine it, be sure to redefine the function
make-auto-save-file-namecorrespondingly.
This function returns the file name to use for auto-saving the current buffer. This is just the file name with hash marks (‘#’) prepended and appended to it. This function does not look at the variable
auto-save-visited-file-name(described below); callers of this function should check that variable first.(make-auto-save-file-name) ⇒ "/xcssun/users/rms/lewis/#backups.texi#"Here is a simplified version of the standard definition of this function:
(defun make-auto-save-file-name () "Return file name to use for auto-saves \ of current buffer.." (if buffer-file-name (concat (file-name-directory buffer-file-name) "#" (file-name-nondirectory buffer-file-name) "#") (expand-file-name (concat "#%" (buffer-name) "#"))))This exists as a separate function so that you can redefine it to customize the naming convention for auto-save files. Be sure to change
auto-save-file-name-pin a corresponding way.
If this variable is non-
nil, Emacs auto-saves buffers in the files they are visiting. That is, the auto-save is done in the same file that you are editing. Normally, this variable isnil, so auto-save files have distinct names that are created bymake-auto-save-file-name.When you change the value of this variable, the new value does not take effect in an existing buffer until the next time auto-save mode is reenabled in it. If auto-save mode is already enabled, auto-saves continue to go in the same file name until
auto-save-modeis called again.
This function returns
tif the current buffer has been auto-saved since the last time it was read in or saved.
This function marks the current buffer as auto-saved. The buffer will not be auto-saved again until the buffer text is changed again. The function returns
nil.
The value of this variable specifies how often to do auto-saving, in terms of number of input events. Each time this many additional input events are read, Emacs does auto-saving for all buffers in which that is enabled. Setting this to zero disables autosaving based on the number of characters typed.
The value of this variable is the number of seconds of idle time that should cause auto-saving. Each time the user pauses for this long, Emacs does auto-saving for all buffers in which that is enabled. (If the current buffer is large, the specified timeout is multiplied by a factor that increases as the size increases; for a million-byte buffer, the factor is almost 4.)
If the value is zero or
nil, then auto-saving is not done as a result of idleness, only after a certain number of input events as specified byauto-save-interval.
If this variable is non-
nil, buffers that are visiting files have auto-saving enabled by default. Otherwise, they do not.
This function auto-saves all buffers that need to be auto-saved. It saves all buffers for which auto-saving is enabled and that have been changed since the previous auto-save.
If any buffers are auto-saved,
do-auto-savenormally displays a message saying ‘Auto-saving...’ in the echo area while auto-saving is going on. However, if no-message is non-nil, the message is inhibited.If current-only is non-
nil, only the current buffer is auto-saved.
This function deletes the current buffer's auto-save file if
delete-auto-save-filesis non-nil. It is called every time a buffer is saved.Unless force is non-
nil, this function only deletes the file if it was written by the current Emacs session since the last true save.
This variable is used by the function
delete-auto-save-file-if-necessary. If it is non-nil, Emacs deletes auto-save files when a true save is done (in the visited file). This saves disk space and unclutters your directory.
This function adjusts the current buffer's auto-save file name if the visited file name has changed. It also renames an existing auto-save file, if it was made in the current Emacs session. If the visited file name has not changed, this function does nothing.
The value of this buffer-local variable is the length of the current buffer, when it was last read in, saved, or auto-saved. This is used to detect a substantial decrease in size, and turn off auto-saving in response.
If it is −1, that means auto-saving is temporarily shut off in this buffer due to a substantial decrease in size. Explicitly saving the buffer stores a positive value in this variable, thus reenabling auto-saving. Turning auto-save mode off or on also updates this variable, so that the substantial decrease in size is forgotten.
If it is −2, that means this buffer should disregard changes in buffer size; in particular, it should not shut off auto-saving temporarily due to changes in buffer size.
This variable (if non-
nil) specifies a file for recording the names of all the auto-save files. Each time Emacs does auto-saving, it writes two lines into this file for each buffer that has auto-saving enabled. The first line gives the name of the visited file (it's empty if the buffer has none), and the second gives the name of the auto-save file.When Emacs exits normally, it deletes this file; if Emacs crashes, you can look in the file to find all the auto-save files that might contain work that was otherwise lost. The
recover-sessioncommand uses this file to find them.The default name for this file specifies your home directory and starts with ‘.saves-’. It also contains the Emacs process ID and the host name.
After Emacs reads your init file, it initializes
auto-save-list-file-name(if you have not already set it non-nil) based on this prefix, adding the host name and process ID. If you set this tonilin your init file, then Emacs does not initializeauto-save-list-file-name.
If you have made extensive changes to a file and then change your mind
about them, you can get rid of them by reading in the previous version
of the file with the revert-buffer command. See Reverting a Buffer.
This command replaces the buffer text with the text of the visited file on disk. This action undoes all changes since the file was visited or saved.
By default, if the latest auto-save file is more recent than the visited file, and the argument ignore-auto is
nil,revert-bufferasks the user whether to use that auto-save instead. When you invoke this command interactively, ignore-auto istif there is no numeric prefix argument; thus, the interactive default is not to check the auto-save file.Normally,
revert-bufferasks for confirmation before it changes the buffer; but if the argument noconfirm is non-nil,revert-bufferdoes not ask for confirmation.Normally, this command reinitializes the buffer's major and minor modes using
normal-mode. But if preserve-modes is non-nil, the modes remain unchanged.Reverting tries to preserve marker positions in the buffer by using the replacement feature of
insert-file-contents. If the buffer contents and the file contents are identical before the revert operation, reverting preserves all the markers. If they are not identical, reverting does change the buffer; in that case, it preserves the markers in the unchanged text (if any) at the beginning and end of the buffer. Preserving any additional markers would be problematical.
You can customize how revert-buffer does its work by setting
the variables described in the rest of this section.
This variable holds a list of files that should be reverted without query. The value is a list of regular expressions. If the visited file name matches one of these regular expressions, and the file has changed on disk but the buffer is not modified, then
revert-bufferreverts the file without asking the user for confirmation.
Some major modes customize revert-buffer by making
buffer-local bindings for these variables:
The value of this variable is the function to use to revert this buffer. If non-
nil, it should be a function with two optional arguments to do the work of reverting. The two optional arguments, ignore-auto and noconfirm, are the arguments thatrevert-bufferreceived. If the value isnil, reverting works the usual way.Modes such as Dired mode, in which the text being edited does not consist of a file's contents but can be regenerated in some other fashion, can give this variable a buffer-local value that is a function to regenerate the contents.
The value of this variable, if non-
nil, specifies the function to use to insert the updated contents when reverting this buffer. The function receives two arguments: first the file name to use; second,tif the user has asked to read the auto-save file.The reason for a mode to set this variable instead of
revert-buffer-functionis to avoid duplicating or replacing the rest of whatrevert-bufferdoes: asking for confirmation, clearing the undo list, deciding the proper major mode, and running the hooks listed below.
This normal hook is run by
revert-bufferbefore inserting the modified contents—but only ifrevert-buffer-functionisnil.
This normal hook is run by
revert-bufferafter inserting the modified contents—but only ifrevert-buffer-functionisnil.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. While several buffers may exist at one time, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. Although several buffers normally exist, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as a string that you can extend; insertions and deletions may occur in any part of the buffer. See Text.
A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is accessible only through special-purpose functions. For example, the visited file name is directly accessible through a variable, while the value of point is accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored in
buffer-local variable bindings, which are variable values that are
effective only in a particular buffer. This feature allows each buffer
to override the values of certain variables. Most major modes override
variables such as fill-column or comment-column in this
way. For more information about buffer-local variables and functions
related to them, see Buffer-Local Variables.
For functions and variables related to visiting files in buffers, see Visiting Files and Saving Buffers. For functions and variables related to the display of buffers in windows, see Buffers and Windows.
There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the current buffer. This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (see Text). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can temporarily designate any buffer as current in order to operate on its contents, without changing what is displayed on the screen.
The way to designate a current buffer in a Lisp program is by calling
set-buffer. The specified buffer remains current until a new one
is designated.
When an editing command returns to the editor command loop, the
command loop designates the buffer displayed in the selected window as
current, to prevent confusion: the buffer that the cursor is in when
Emacs reads a command is the buffer that the command will apply to.
(See Command Loop.) Therefore, set-buffer is not the way to
switch visibly to a different buffer so that the user can edit it. For
that, you must use the functions described in Displaying Buffers.
Warning: Lisp functions that change to a different current buffer
should not depend on the command loop to set it back afterwards.
Editing commands written in Emacs Lisp can be called from other programs
as well as from the command loop; it is convenient for the caller if
the subroutine does not change which buffer is current (unless, of
course, that is the subroutine's purpose). Therefore, you should
normally use set-buffer within a save-current-buffer or
save-excursion (see Excursions) form that will restore the
current buffer when your function is done. Here, as an example, is a
simplified version of the command append-to-buffer:
(defun append-to-buffer (buffer start end)
"Append to specified buffer the text of the region."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-current-buffer
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
This function binds a local variable to record the current buffer, and
then save-current-buffer arranges to make it current again.
Next, set-buffer makes the specified buffer current. Finally,
insert-buffer-substring copies the string from the original
current buffer to the specified (and now current) buffer.
If the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed.
If you make local bindings (with let or function arguments) for
a variable that may also have buffer-local bindings, make sure that the
same buffer is current at the beginning and at the end of the local
binding's scope. Otherwise you might bind it in one buffer and unbind
it in another! There are two ways to do this. In simple cases, you may
see that nothing ever changes the current buffer within the scope of the
binding. Otherwise, use save-current-buffer or
save-excursion to make sure that the buffer current at the
beginning is current again whenever the variable is unbound.
Do not rely on using set-buffer to change the current buffer
back, because that won't do the job if a quit happens while the wrong
buffer is current. For instance, in the previous example, it would
have been wrong to do this:
(let ((oldbuf (current-buffer)))
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end)
(set-buffer oldbuf))
Using save-current-buffer, as we did, handles quitting, errors,
and throw, as well as ordinary evaluation.
This function returns the current buffer.
(current-buffer) ⇒ #<buffer buffers.texi>
This function makes buffer-or-name the current buffer. buffer-or-name must be an existing buffer or the name of an existing buffer. The return value is the buffer made current.
This function does not display the buffer in any window, so the user cannot necessarily see the buffer. But Lisp programs will now operate on it.
The
save-current-bufferspecial form saves the identity of the current buffer, evaluates the body forms, and finally restores that buffer as current. The return value is the value of the last form in body. The current buffer is restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).If the buffer that used to be current has been killed by the time of exit from
save-current-buffer, then it is not made current again, of course. Instead, whichever buffer was current just before exit remains current.
The
with-current-buffermacro saves the identity of the current buffer, makes buffer-or-name current, evaluates the body forms, and finally restores the current buffer. buffer-or-name must specify an existing buffer or the name of an existing buffer.The return value is the value of the last form in body. The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).
The
with-temp-buffermacro evaluates the body forms with a temporary buffer as the current buffer. It saves the identity of the current buffer, creates a temporary buffer and makes it current, evaluates the body forms, and finally restores the previous current buffer while killing the temporary buffer. By default, undo information (see Undo) is not recorded in the buffer created by this macro (but body can enable that, if needed).The return value is the value of the last form in body. You can return the contents of the temporary buffer by using
(buffer-string)as the last form.The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).See also
with-temp-filein Writing to Files.
Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer must be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the list-buffers and
buffer-menu commands don't mention them (but if such a buffer
visits a file, it is mentioned). A name starting with
space also initially disables recording undo information; see
Undo.
This function returns the name of buffer as a string. buffer defaults to the current buffer.
If
buffer-namereturnsnil, it means that buffer has been killed. See Killing Buffers.(buffer-name) ⇒ "buffers.texi" (setq foo (get-buffer "temp")) ⇒ #<buffer temp> (kill-buffer foo) ⇒ nil (buffer-name foo) ⇒ nil foo ⇒ #<killed buffer>
This function renames the current buffer to newname. An error is signaled if newname is not a string.
Ordinarily,
rename-buffersignals an error if newname is already in use. However, if unique is non-nil, it modifies newname to make a name that is not in use. Interactively, you can make unique non-nilwith a numeric prefix argument. (This is how the commandrename-uniquelyis implemented.)This function returns the name actually given to the buffer.
This function returns the buffer specified by buffer-or-name. If buffer-or-name is a string and there is no buffer with that name, the value is
nil. If buffer-or-name is a buffer, it is returned as given; that is not very useful, so the argument is usually a name. For example:(setq b (get-buffer "lewis")) ⇒ #<buffer lewis> (get-buffer b) ⇒ #<buffer lewis> (get-buffer "Frazzle-nots") ⇒ nilSee also the function
get-buffer-createin Creating Buffers.
This function returns a name that would be unique for a new buffer—but does not create the buffer. It starts with starting-name, and produces a name not currently in use for any buffer by appending a number inside of ‘<...>’. It starts at 2 and keeps incrementing the number until it is not the name of an existing buffer.
If the optional second argument ignore is non-
nil, it should be a string, a potential buffer name. It means to consider that potential buffer acceptable, if it is tried, even it is the name of an existing buffer (which would normally be rejected). Thus, if buffers named ‘foo’, ‘foo<2>’, ‘foo<3>’ and ‘foo<4>’ exist,(generate-new-buffer-name "foo") ⇒ "foo<5>" (generate-new-buffer-name "foo" "foo<3>") ⇒ "foo<3>" (generate-new-buffer-name "foo" "foo<6>") ⇒ "foo<5>"See the related function
generate-new-bufferin Creating Buffers.
The buffer file name is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file name
is nil. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently.
See Visiting Files.
This function returns the absolute file name of the file that buffer is visiting. If buffer is not visiting any file,
buffer-file-namereturnsnil. If buffer is not supplied, it defaults to the current buffer.(buffer-file-name (other-buffer)) ⇒ "/usr/user/lewis/manual/files.texi"
This buffer-local variable contains the name of the file being visited in the current buffer, or
nilif it is not visiting a file. It is a permanent local variable, unaffected bykill-all-local-variables.buffer-file-name ⇒ "/usr/user/lewis/manual/buffers.texi"It is risky to change this variable's value without doing various other things. Normally it is better to use
set-visited-file-name(see below); some of the things done there, such as changing the buffer name, are not strictly necessary, but others are essential to avoid confusing Emacs.
This buffer-local variable holds the abbreviated truename of the file visited in the current buffer, or
nilif no file is visited. It is a permanent local, unaffected bykill-all-local-variables. See Truenames, and Definition of abbreviate-file-name.
This buffer-local variable holds the file number and directory device number of the file visited in the current buffer, or
nilif no file or a nonexistent file is visited. It is a permanent local, unaffected bykill-all-local-variables.The value is normally a list of the form
(filenum devnum). This pair of numbers uniquely identifies the file among all files accessible on the system. See the functionfile-attributes, in File Attributes, for more information about them.If
buffer-file-nameis the name of a symbolic link, then both numbers refer to the recursive target.
This function returns the buffer visiting file filename. If there is no such buffer, it returns
nil. The argument filename, which must be a string, is expanded (see File Name Expansion), then compared against the visited file names of all live buffers. Note that the buffer'sbuffer-file-namemust match the expansion of filename exactly. This function will not recognize other names for the same file.(get-file-buffer "buffers.texi") ⇒ #<buffer buffers.texi>In unusual circumstances, there can be more than one buffer visiting the same file name. In such cases, this function returns the first such buffer in the buffer list.
This is like
get-file-buffer, except that it can return any buffer visiting the file possibly under a different name. That is, the buffer'sbuffer-file-namedoes not need to match the expansion of filename exactly, it only needs to refer to the same file. If predicate is non-nil, it should be a function of one argument, a buffer visiting filename. The buffer is only considered a suitable return value if predicate returns non-nil. If it can not find a suitable buffer to return,find-buffer-visitingreturnsnil.
If filename is a non-empty string, this function changes the name of the file visited in the current buffer to filename. (If the buffer had no visited file, this gives it one.) The next time the buffer is saved it will go in the newly-specified file.
This command marks the buffer as modified, since it does not (as far as Emacs knows) match the contents of filename, even if it matched the former visited file. It also renames the buffer to correspond to the new file name, unless the new name is already in use.
If filename is
nilor the empty string, that stands for “no visited file.” In this case,set-visited-file-namemarks the buffer as having no visited file, without changing the buffer's modified flag.Normally, this function asks the user for confirmation if there already is a buffer visiting filename. If no-query is non-
nil, that prevents asking this question. If there already is a buffer visiting filename, and the user confirms or query is non-nil, this function makes the new buffer name unique by appending a number inside of ‘<...>’ to filename.If along-with-file is non-
nil, that means to assume that the former visited file has been renamed to filename. In this case, the command does not change the buffer's modified flag, nor the buffer's recorded last file modification time as reported byvisited-file-modtime(see Modification Time). If along-with-file isnil, this function clears the recorded last file modification time, after whichvisited-file-modtimereturns zero.When the function
set-visited-file-nameis called interactively, it prompts for filename in the minibuffer.
This buffer-local variable specifies a string to display in a buffer listing where the visited file name would go, for buffers that don't have a visited file name. Dired buffers use this variable.
Emacs keeps a flag called the modified flag for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to t whenever you alter the contents of the buffer, and
cleared to nil when you save it. Thus, the flag shows whether
there are unsaved changes. The flag value is normally shown in the mode
line (see Mode Line Variables), and controls saving (see Saving Buffers) and auto-saving (see Auto-Saving).
Some Lisp programs set the flag explicitly. For example, the function
set-visited-file-name sets the flag to t, because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.
The functions that modify the contents of buffers are described in Text.
This function returns
tif the buffer buffer has been modified since it was last read in from a file or saved, ornilotherwise. If buffer is not supplied, the current buffer is tested.
This function marks the current buffer as modified if flag is non-
nil, or as unmodified if the flag isnil.Another effect of calling this function is to cause unconditional redisplay of the mode line for the current buffer. In fact, the function
force-mode-line-updateworks by doing this:(set-buffer-modified-p (buffer-modified-p))
Like
set-buffer-modified-p, but does not force redisplay of mode lines.
This command marks the current buffer as unmodified, and not needing to be saved. If arg is non-
nil, it marks the buffer as modified, so that it will be saved at the next suitable occasion. Interactively, arg is the prefix argument.Don't use this function in programs, since it prints a message in the echo area; use
set-buffer-modified-p(above) instead.
This function returns buffer's modification-count. This is a counter that increments every time the buffer is modified. If buffer is
nil(or omitted), the current buffer is used. The counter can wrap around occasionally.
This function returns buffer's character-change modification-count. Changes to text properties leave this counter unchanged; however, each time text is inserted or removed from the buffer, the counter is reset to the value that would be returned by
buffer-modified-tick. By comparing the values returned by twobuffer-chars-modified-tickcalls, you can tell whether a character change occurred in that buffer in between the calls. If buffer isnil(or omitted), the current buffer is used.
Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file's modification time using the functions described below before saving the file. (See File Attributes, for how to examine a file's modification time.)
This function compares what buffer has recorded for the modification time of its visited file against the actual modification time of the file as recorded by the operating system. The two should be the same unless some other process has written the file since Emacs visited or saved it.
The function returns
tif the last actual modification time and Emacs's recorded modification time are the same,nilotherwise. It also returnstif the buffer has no recorded last modification time, that is ifvisited-file-modtimewould return zero.It always returns
tfor buffers that are not visiting a file, even ifvisited-file-modtimereturns a non-zero value. For instance, it always returnstfor dired buffers. It returnstfor buffers that are visiting a file that does not exist and never existed, butnilfor file-visiting buffers whose file has been deleted.
This function clears out the record of the last modification time of the file being visited by the current buffer. As a result, the next attempt to save this buffer will not complain of a discrepancy in file modification times.
This function is called in
set-visited-file-nameand other exceptional places where the usual test to avoid overwriting a changed file should not be done.
This function returns the current buffer's recorded last file modification time, as a list of the form
(high low). (This is the same format thatfile-attributesuses to return time values; see File Attributes.)If the buffer has no recorded last modification time, this function returns zero. This case occurs, for instance, if the buffer is not visiting a file or if the time has been explicitly cleared by
clear-visited-file-modtime. Note, however, thatvisited-file-modtimereturns a list for some non-file buffers too. For instance, in a Dired buffer listing a directory, it returns the last modification time of that directory, as recorded by Dired.For a new buffer visiting a not yet existing file, high is −1 and low is 65535, that is, 2**16 - 1.
This function updates the buffer's record of the last modification time of the visited file, to the value specified by time if time is not
nil, and otherwise to the last modification time of the visited file.If time is neither
nilnor zero, it should have the form(high.low)or(high low), in either case containing two integers, each of which holds 16 bits of the time.This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason.
This function is used to ask a user how to proceed after an attempt to modify an buffer visiting file filename when the file is newer than the buffer text. Emacs detects this because the modification time of the file on disk is newer than the last save-time of the buffer. This means some other program has probably altered the file.
Depending on the user's answer, the function may return normally, in which case the modification of the buffer proceeds, or it may signal a
file-supersessionerror with data(filename), in which case the proposed buffer modification is not allowed.This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file userlock.el for the standard definition.
See also the file locking mechanism in File Locks.
If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing.
Read-only buffers are used in two kinds of situations:
Here, the purpose is to inform the user that editing the buffer with the aim of saving it in the file may be futile or undesirable. The user who wants to change the buffer text despite this can do so after clearing the read-only flag with C-x C-q.
The special commands of these modes bind buffer-read-only to
nil (with let) or bind inhibit-read-only to
t around the places where they themselves change the text.
This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-
nil.
If this variable is non-
nil, then read-only buffers and, depending on the actual value, some or all read-only characters may be modified. Read-only characters in a buffer are those that have non-nilread-onlyproperties (either text properties or overlay properties). See Special Properties, for more information about text properties. See Overlays, for more information about overlays and their properties.If
inhibit-read-onlyist, allread-onlycharacter properties have no effect. Ifinhibit-read-onlyis a list, thenread-onlycharacter properties have no effect if they are members of the list (comparison is done witheq).
This command toggles whether the current buffer is read-only. It is intended for interactive use; do not use it in programs. At any given point in a program, you should know whether you want the read-only flag on or off; so you can set
buffer-read-onlyexplicitly to the proper value,tornil.If arg is non-
nil, it should be a raw prefix argument.toggle-read-onlysetsbuffer-read-onlytotif the numeric value of that prefix argument is positive and tonilotherwise. See Prefix Command Arguments.
This function signals a
buffer-read-onlyerror if the current buffer is read-only. See Using Interactive, for another way to signal an error if the current buffer is read-only.
The buffer list is a list of all live buffers. The order of the
buffers in this list is based primarily on how recently each buffer has
been displayed in a window. Several functions, notably
other-buffer, use this ordering. A buffer list displayed for the
user also follows this order.
Creating a buffer adds it to the end of the buffer list, and killing a
buffer removes it from that list. A buffer moves to the front of this
list whenever it is chosen for display in a window (see Displaying Buffers) or a window displaying it is selected (see Selecting Windows). A buffer moves to the end of the list when it is buried (see
bury-buffer, below). There are no functions available to the
Lisp programmer which directly manipulate the buffer list.
In addition to the fundamental buffer list just described, Emacs
maintains a local buffer list for each frame, in which the buffers that
have been displayed (or had their windows selected) in that frame come
first. (This order is recorded in the frame's buffer-list frame
parameter; see Buffer Parameters.) Buffers never displayed in
that frame come afterward, ordered according to the fundamental buffer
list.
This function returns the buffer list, including all buffers, even those whose names begin with a space. The elements are actual buffers, not their names.
If frame is a frame, this returns frame's local buffer list. If frame is
nilor omitted, the fundamental buffer list is used: the buffers appear in order of most recent display or selection, regardless of which frames they were displayed on.(buffer-list) ⇒ (#<buffer buffers.texi> #<buffer *Minibuf-1*> #<buffer buffer.c> #<buffer *Help*> #<buffer TAGS>) ;; Note that the name of the minibuffer ;; begins with a space! (mapcar (function buffer-name) (buffer-list)) ⇒ ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS")
The list returned by buffer-list is constructed specifically;
it is not an internal Emacs data structure, and modifying it has no
effect on the order of buffers. If you want to change the order of
buffers in the fundamental buffer list, here is an easy way:
(defun reorder-buffer-list (new-list)
(while new-list
(bury-buffer (car new-list))
(setq new-list (cdr new-list))))
With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer.
To change the order or value of a specific frame's buffer list, set
that frame's buffer-list parameter with
modify-frame-parameters (see Parameter Access).
This function returns the first buffer in the buffer list other than buffer. Usually, this is the buffer appearing in the most recently selected window (in frame frame or else the selected frame, see Input Focus), aside from buffer. Buffers whose names start with a space are not considered at all.
If buffer is not supplied (or if it is not a live buffer), then
other-bufferreturns the first buffer in the selected frame's local buffer list. (If frame is non-nil, it returns the first buffer in frame's local buffer list instead.)If frame has a non-
nilbuffer-predicateparameter, thenother-bufferuses that predicate to decide which buffers to consider. It calls the predicate once for each buffer, and if the value isnil, that buffer is ignored. See Buffer Parameters.If visible-ok is
nil,other-bufferavoids returning a buffer visible in any window on any visible frame, except as a last resort. If visible-ok is non-nil, then it does not matter whether a buffer is displayed somewhere or not.If no suitable buffer exists, the buffer ‘*scratch*’ is returned (and created, if necessary).
This function returns the last buffer in frame's buffer list other than BUFFER. If frame is omitted or
nil, it uses the selected frame's buffer list.The argument visible-ok is handled as with
other-buffer, see above. If no suitable buffer can be found, the buffer ‘*scratch*’ is returned.
This command puts buffer-or-name at the end of the buffer list, without changing the order of any of the other buffers on the list. This buffer therefore becomes the least desirable candidate for
other-bufferto return. The argument can be either a buffer itself or the name of one.
bury-bufferoperates on each frame'sbuffer-listparameter as well as the fundamental buffer list; therefore, the buffer that you bury will come last in the value of(buffer-listframe)and in the value of(buffer-list).If buffer-or-name is
nilor omitted, this means to bury the current buffer. In addition, if the buffer is displayed in the selected window, this switches to some other buffer (obtained usingother-buffer) in the selected window. See Displaying Buffers. But if the selected window is dedicated to its buffer, it deletes that window if there are other windows left on its frame. Otherwise, if the selected window is the only window on its frame, it iconifies that frame. If buffer-or-name is displayed in some other window, it remains displayed there.To replace a buffer in all the windows that display it, use
replace-buffer-in-windows. See Buffers and Windows.
This command switches to the last buffer in the local buffer list of the selected frame. More precisely, it calls the function
switch-to-buffer(see Displaying Buffers), to display the buffer returned bylast-buffer, see above, in the selected window.
This section describes the two primitives for creating buffers.
get-buffer-create creates a buffer if it finds no existing buffer
with the specified name; generate-new-buffer always creates a new
buffer and gives it a unique name.
Other functions you can use to create buffers include
with-output-to-temp-buffer (see Temporary Displays) and
create-file-buffer (see Visiting Files). Starting a
subprocess can also create a buffer (see Processes).
This function returns a buffer named buffer-or-name. The buffer returned does not become the current buffer—this function does not change which buffer is current.
buffer-or-name must be either a string or an existing buffer. If it is a string and a live buffer with that name already exists,
get-buffer-createreturns that buffer. If no such buffer exists, it creates a new buffer. If buffer-or-name is a buffer instead of a string, it is returned as given, even if it is dead.(get-buffer-create "foo") ⇒ #<buffer foo>The major mode for a newly created buffer is set to Fundamental mode. (The default value of the variable
major-modeis handled at a higher level; see Auto Major Mode.) If the name begins with a space, the buffer initially disables undo information recording (see Undo).
This function returns a newly created, empty buffer, but does not make it current. If there is no buffer named name, then that is the name of the new buffer. If that name is in use, this function adds suffixes of the form ‘<n>’ to name, where n is an integer. It tries successive integers starting with 2 until it finds an available name.
An error is signaled if name is not a string.
(generate-new-buffer "bar") ⇒ #<buffer bar> (generate-new-buffer "bar") ⇒ #<buffer bar<2>> (generate-new-buffer "bar") ⇒ #<buffer bar<3>>The major mode for the new buffer is set to Fundamental mode. The default value of the variable
major-modeis handled at a higher level. See Auto Major Mode.See the related function
generate-new-buffer-namein Buffer Names.
Killing a buffer makes its name unknown to Emacs and makes the memory space it occupied available for other use.
The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
their identity, however; if you kill two distinct buffers, they remain
distinct according to eq although both are dead.
If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can in general change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). See Current Buffer.
If you kill a buffer that is the base buffer of one or more indirect buffers, the indirect buffers are automatically killed as well.
The buffer-name of a killed buffer is nil. You can use
this feature to test whether a buffer has been killed:
(defun buffer-killed-p (buffer)
"Return t if BUFFER is killed."
(not (buffer-name buffer)))
This function kills the buffer buffer-or-name, freeing all its memory for other uses or to be returned to the operating system. If buffer-or-name is
nilor omitted, it kills the current buffer.Any processes that have this buffer as the
process-bufferare sent theSIGHUPsignal, which normally causes them to terminate. (The basic meaning ofSIGHUPis that a dialup line has been disconnected.) See Signals to Processes.If the buffer is visiting a file and contains unsaved changes,
kill-bufferasks the user to confirm before the buffer is killed. It does this even if not called interactively. To prevent the request for confirmation, clear the modified flag before callingkill-buffer. See Buffer Modification.This function calls
replace-buffer-in-windowsfor cleaning up all windows currently displaying the buffer to be killed.Killing a buffer that is already dead has no effect.
This function returns
tif it actually killed the buffer. It returnsnilif the user refuses to confirm or if buffer-or-name was already dead.(kill-buffer "foo.unchanged") ⇒ t (kill-buffer "foo.changed") ---------- Buffer: Minibuffer ---------- Buffer foo.changed modified; kill anyway? (yes or no) yes ---------- Buffer: Minibuffer ---------- ⇒ t
After confirming unsaved changes,
kill-buffercalls the functions in the listkill-buffer-query-functions, in order of appearance, with no arguments. The buffer being killed is the current buffer when they are called. The idea of this feature is that these functions will ask for confirmation from the user. If any of them returnsnil,kill-bufferspares the buffer's life.
This is a normal hook run by
kill-bufferafter asking all the questions it is going to ask, just before actually killing the buffer. The buffer to be killed is current when the hook functions run. See Hooks. This variable is a permanent local, so its local binding is not cleared by changing major modes.
This variable, if non-
nilin a particular buffer, tellssave-buffers-kill-emacsandsave-some-buffers(if the second optional argument to that function ist) to offer to save that buffer, just as they offer to save file-visiting buffers. See Definition of save-some-buffers. The variablebuffer-offer-saveautomatically becomes buffer-local when set for any reason. See Buffer-Local Variables.
This variable, if non-
nilin a particular buffer, tellssave-buffers-kill-emacsandsave-some-buffersto save this buffer (if it's modified) without asking the user. The variable automatically becomes buffer-local when set for any reason.
This function returns
tif object is a buffer which has not been killed,nilotherwise.
An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves.
In all other respects, the indirect buffer and its base buffer are completely separate. They have different names, independent values of point, independent narrowing, independent markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), independent major modes, and independent buffer-local variable bindings.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually saves the base buffer.
Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer.
This creates and returns an indirect buffer named name whose base buffer is base-buffer. The argument base-buffer may be a live buffer or the name (a string) of an existing buffer. If name is the name of an existing buffer, an error is signaled.
If clone is non-
nil, then the indirect buffer originally shares the “state” of base-buffer such as major mode, minor modes, buffer local variables and so on. If clone is omitted ornilthe indirect buffer's state is set to the default state for new buffers.If base-buffer is an indirect buffer, its base buffer is used as the base for the new buffer. If, in addition, clone is non-
nil, the initial state is copied from the actual base buffer, not from base-buffer.
This function creates and returns a new indirect buffer that shares the current buffer's base buffer and copies the rest of the current buffer's attributes. (If the current buffer is not indirect, it is used as the base buffer.)
If display-flag is non-
nil, that means to display the new buffer by callingpop-to-buffer. If norecord is non-nil, that means not to put the new buffer to the front of the buffer list.
This function returns the base buffer of buffer, which defaults to the current buffer. If buffer is not indirect, the value is
nil. Otherwise, the value is another buffer, which is never an indirect buffer.
Specialized modes sometimes need to let the user access from the same buffer several vastly different types of text. For example, you may need to display a summary of the buffer text, in addition to letting the user access the text itself.
This could be implemented with multiple buffers (kept in sync when the user edits the text), or with narrowing (see Narrowing). But these alternatives might sometimes become tedious or prohibitively expensive, especially if each type of text requires expensive buffer-global operations in order to provide correct display and editing commands.
Emacs provides another facility for such modes: you can quickly swap
buffer text between two buffers with buffer-swap-text. This
function is very fast because it doesn't move any text, it only
changes the internal data structures of the buffer object to point to
a different chunk of text. Using it, you can pretend that a group of
two or more buffers are actually a single virtual buffer that holds
the contents of all the individual buffers together.
This function swaps the text of the current buffer and that of its argument buffer. It signals an error if one of the two buffers is an indirect buffer (see Indirect Buffers) or is a base buffer of an indirect buffer.
All the buffer properties that are related to the buffer text are swapped as well: the positions of point and mark, all the markers, the overlays, the text properties, the undo list, the value of the
enable-multibyte-charactersflag (see enable-multibyte-characters), etc.
If you use buffer-swap-text on a file-visiting buffer, you
should set up a hook to save the buffer's original text rather than
what it was swapped with. write-region-annotate-functions
works for this purpose. You should probably set
buffer-saved-size to −2 in the buffer, so that changes
in the text it is swapped with will not interfere with auto-saving.
Emacs buffers are implemented using an invisible gap to make insertion and deletion faster. Insertion works by filling in part of the gap, and deletion adds to the gap. Of course, this means that the gap must first be moved to the locus of the insertion or deletion. Emacs moves the gap only when you try to insert or delete. This is why your first editing command in one part of a large buffer, after previously editing in another far-away part, sometimes involves a noticeable delay.
This mechanism works invisibly, and Lisp code should never be affected by the gap's current location, but these functions are available for getting information about the gap status.
This chapter describes most of the functions and variables related to Emacs windows. See Frames and Windows, for how windows relate to frames. See Display, for information on how text is displayed in windows.
A window in Emacs is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object that represents that screen area in Emacs Lisp. It should be clear from the context which is meant.
Emacs groups windows into frames; see Frames. A frame represents an area of screen available for Emacs to use. Each frame always contains at least one window, but you can subdivide it vertically or horizontally into multiple, nonoverlapping Emacs windows.
In each frame, at any time, one and only one window is designated as
selected within the frame. The frame's cursor appears in that
window, but the other windows have “non-selected” cursors, normally
less visible. (See Cursor Parameters, for customizing this.) At
any time, one frame is the selected frame; and the window selected
within that frame is the selected window. The selected window's
buffer is usually the current buffer (except when set-buffer has
been used); see Current Buffer.
For practical purposes, a window exists only while it is displayed in a frame. Once removed from the frame, the window is effectively deleted and should not be used, even though there may still be references to it from other Lisp objects; see Deleting Windows. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life; see Window Configurations.
Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to display related information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached.
The meaning of “window” in Emacs is similar to what it means in the context of general-purpose window systems such as X, but not identical. The X Window System places X windows on the screen; Emacs uses one or more X windows as frames, and subdivides them into Emacs windows. When you use Emacs on a character-only terminal, Emacs treats the whole terminal screen as one frame.
Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are tiled; they never overlap, and together they fill the whole screen or frame. Because of the way in which Emacs creates new windows (see Splitting Windows) and resizes them (see Resizing Windows), not all conceivable tilings of windows on an Emacs frame are actually possible.
The functions described below are the primitives used to split a window into two windows. They do not accept a buffer as an argument. Rather, the two “halves” of the split window initially display the same buffer previously visible in the window that was split.
This function splits a new window out of window's screen area. It returns the new window. The default for window is the selected window. When you split the selected window, it remains selected.
If horizontal is non-
nil, then window splits into two side by side windows. The original window keeps the leftmost size columns, and gives the rest of the columns to the new window. Otherwise, window splits into windows one above the other, the original window keeps the upper size lines and gives the rest of the lines to the new window. The original window window is therefore the left-hand or upper of the two, and the new window is the right-hand or lower.If size is omitted or
nil, then window is divided evenly into two parts. (If there is an odd line, it is allocated to the new window.) Whensplit-windowis called interactively, all its arguments arenil.If splitting would result in making a window that is smaller than
window-min-heightorwindow-min-width(see Resizing Windows),split-windowsignals an error and does not split the window at all.The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then it splits the window.
(setq w (selected-window)) ⇒ #<window 8 on windows.texi> (window-edges) ; Edges in order: ⇒ (0 0 80 50) ; left--top--right--bottom ;; Returns window created (setq w2 (split-window w 15)) ⇒ #<window 28 on windows.texi> (window-edges w2) ⇒ (0 15 80 50) ; Bottom window; ; top is line 15 (window-edges w) ⇒ (0 0 80 15) ; Top windowThe screen looks like this:
__________ | | line 0 | w | |__________| | | line 15 | w2 | |__________| line 50 column 0 column 80Next, split the top window horizontally:
(setq w3 (split-window w 35 t)) ⇒ #<window 32 on windows.texi> (window-edges w3) ⇒ (35 0 80 15) ; Left edge at column 35 (window-edges w) ⇒ (0 0 35 15) ; Right edge at column 35 (window-edges w2) ⇒ (0 15 80 50) ; Bottom window unchangedNow the screen looks like this:
column 35 __________ | | | line 0 | w | w3 | |___|______| | | line 15 | w2 | |__________| line 50 column 0 column 80Normally, Emacs indicates the border between two side-by-side windows with a scroll bar (see Scroll Bars), or with ‘|’ characters. The display table can specify alternative border characters; see Display Tables.
This function splits the selected window into two windows, one above the other, leaving the upper of the two windows selected, with size lines. (If size is negative, then the lower of the two windows gets −size lines and the upper window gets the rest, but the upper window is still the one selected.) However, if
split-window-keep-point(see below) isnil, then either window can be selected.In other respects, this function is similar to
split-window. In particular, the upper window is the original one and the return value is the new, lower window.
If this variable is non-
nil(the default), thensplit-window-verticallybehaves as described above.If it is
nil, thensplit-window-verticallyadjusts point in each of the two windows to avoid scrolling. (This is useful on slow terminals.) It selects whichever window contains the screen line that point was previously on.This variable affects the behavior of
split-window-verticallyonly. It has no effect on the other functions described here.
This function splits the selected window into two windows side-by-side, leaving the selected window on the left with size columns. If size is negative, the rightmost window gets −size columns, but the leftmost window still remains selected.
This function is basically an interface to
split-window. You could define a simplified version of the function like this:(defun split-window-horizontally (&optional arg) "Split selected window into two windows, side by side..." (interactive "P") (let ((size (and arg (prefix-numeric-value arg)))) (and size (< size 0) (setq size (+ (window-width) size))) (split-window nil size t)))
This function returns non-
nilif there is only one window. The argument no-mini, if non-nil, means don't count the minibuffer even if it is active; otherwise, the minibuffer window is counted when it is active.The argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil- Count the windows in the selected frame, plus the minibuffer used by that frame even if it lies in some other frame.
t- Count all windows in all existing frames.
visible- Count all windows in all visible frames.
- 0
- Count all windows in all visible or iconified frames.
- anything else
- Count precisely the windows in the selected frame, and no others.
A window remains visible on its frame unless you delete it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (see Window Configurations). Restoring a window configuration also deletes any windows that aren't part of that configuration.
When you delete a window, the space it took up is given to one of its sibling windows adjacent to it.
This function returns
nilif window is deleted, andtotherwise.Warning: Erroneous information or fatal errors may result from using a deleted window as if it were live.
This function removes window from display and returns
nil. The default for window is the selected window. An error is signaled if window is the only window on its frame.
This function makes window the only window on its frame, by deleting the other windows in that frame. The default for window is the selected window. The return value is
nil.
This function deletes all windows showing buffer-or-name. If there are no windows showing buffer-or-name, it does nothing. The optional argument buffer-or-name may be a buffer or the name of an existing buffer and defaults to the current buffer.
delete-windows-onoperates frame by frame. If a frame has several windows showing different buffers, then those showing buffer-or-name are removed, and the others expand to fill the space. If all windows in some frame are showing buffer-or-name (including the case where there is only one window), then the frame winds up with a single window showing another buffer chosen withother-buffer(see The Buffer List). If, however, the window showing buffer-or-name is dedicated to its buffer (see Dedicated Windows), and there are other frames left, that window's frame is deleted.The optional argument frame specifies which frames to operate on. This function does not use it in quite the same way as the other functions which scan all windows; specifically, the values
tandnilhave the opposite of their meanings in other functions. Here are the full details:
- If it is
nil, operate on all frames.- If it is
t, operate on the selected frame.- If it is
visible, operate on all visible frames.- If it is 0, operate on all visible or iconified frames.
- If it is a frame, operate on that frame.
This function always returns
nil.
When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it.
This function returns the selected window. This is the window in which the cursor appears and to which many commands apply.
This function makes window the selected window. The cursor then appears in window (after redisplay). Unless window was already selected,
select-windowmakes window's buffer the current buffer. The return value is window.Normally, window's selected buffer is moved to the front of the buffer list (see The Buffer List) and window becomes the most recently selected window. But if norecord is non-
nil, the buffer list remains unchanged and window does not become the most recently selected one.(setq w (next-window)) (select-window w) ⇒ #<window 65 on windows.texi>
This macro records the selected frame, as well as the selected window of each frame, executes forms in sequence, then restores the earlier selected frame and windows. It also saves and restores the current buffer. It returns the value of the last form in forms.
This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if forms change them, the change persists. If the previously selected window of some frame is no longer live at the time of exit from forms, that frame's selected window is left alone. If the previously selected window is no longer live, then whatever window is selected at the end of forms remains selected. The current buffer is restored if and only if it is still live when exiting forms.
This macro changes neither the ordering of recently selected windows nor the buffer list.
This macro selects window, executes forms in sequence, then restores the previously selected window and current buffer. The ordering of recently selected windows and the buffer list remain unchanged unless you deliberately change them within forms, for example, by calling
select-windowwith argument norecordnil.
The following functions choose one of the windows on the screen, offering various criteria for the choice.
This function returns the window least recently “used” (that is, selected) among a set of candidate windows. If any full-width windows are present, it only considers these.
The selected window is returned if it is the only candidate. A minibuffer window is never a candidate. A dedicated window (see Dedicated Windows) is never a candidate unless the optional argument dedicated is non-
nil.The optional argument frame specifies which windows are considered.
- If it is
nil, consider windows on the selected frame.- If it is
t, consider windows on all frames.- If it is
visible, consider windows on all visible frames.- If it is 0, consider windows on all visible or iconified frames.
- If it is a frame, consider windows on that frame.
This function returns the window with the largest area (height times width). If there are no side-by-side windows, then this is the window with the most lines. A minibuffer window is never a candidate. A dedicated window (see Dedicated Windows) is never a candidate unless the optional argument dedicated is non-
nil.If there are two candidate windows of the same size, this function prefers the one that comes first in the cyclic ordering of windows, starting from the selected window (see Cyclic Window Ordering).
The optional argument frame specifies which set of windows to consider, see
get-lru-windowabove.
This function returns a window satisfying predicate. It cycles through all visible windows using
walk-windows(see Cyclic Window Ordering), calling predicate on each one of them with that window as its argument. The function returns the first window for which predicate returns a non-nilvalue; if that never happens, it returns default (which defaults tonil).The optional arguments minibuf and all-frames specify the set of windows to include in the scan. See the description of
next-windowin Cyclic Window Ordering, for details.
When you use the command C-x o (other-window) to select
some other window, it moves through the windows on the screen in a
specific order. For any given configuration of windows, this order
never varies. It is called the cyclic ordering of windows.
For a particular frame, this ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which windows were split.
If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree (see Window Tree), the order is left to right, or top to bottom.
This function returns the window following window in the cyclic ordering of windows. This is the window C-x o selects if typed when window is selected. The default for window is the selected window.
The value of the optional argument minibuf specifies whether the minibuffer is included in the window order. Normally, when minibuf is
nil, the minibuffer is included only if it is currently “active”; this matches the behavior of C-x o. (The minibuffer window is active while the minibuffer is in use; see Minibuffers.)If minibuf is
t, the cyclic ordering includes the minibuffer window even if it is not active. If minibuf is neithertnornil, the minibuffer window is not included even if it is active.The optional argument all-frames specifies which frames to consider. Here are the possible values and their meanings:
nil- Consider all the windows in window's frame, plus the minibuffer used by that frame even if it lies in some other frame. If the minibuffer counts (as determined by minibuf), then all windows on all frames that share that minibuffer count too.
t- Consider all windows in all existing frames.
visible- Consider all windows in all visible frames. (To get useful results, you must ensure window is in a visible frame.)
- 0
- Consider all windows in all visible or iconified frames.
- a frame
- Consider all windows on that frame.
- anything else
- Consider precisely the windows in window's frame, and no others.
This example assumes there are two windows, both displaying the buffer ‘windows.texi’:
(selected-window) ⇒ #<window 56 on windows.texi> (next-window (selected-window)) ⇒ #<window 52 on windows.texi> (next-window (next-window (selected-window))) ⇒ #<window 56 on windows.texi>
This function returns the window preceding window in the cyclic ordering of windows. The other arguments specify which windows to include in the cycle, as in
next-window.
This function selects another window in the cyclic ordering of windows. count specifies the number of windows to skip in the ordering, starting with the selected window, before making the selection. If count is a positive number, it skips count windows forwards. count negative means skip −count windows backwards. If count is zero, it does not skip any window, thus re-selecting the selected window. In an interactive call, count is the numeric prefix argument.
The optional argument all-frames has the same meaning as in
next-window, but the minibuf argument ofnext-windowis always effectivelynil. This function returnsnil.
This function cycles through all windows. It calls the function
proconce for each window, with the window as its sole argument.The optional arguments minibuf and all-frames specify the set of windows to include in the walk. See
next-window, above, for details.
This function returns a list of all windows on frame, starting with window. The default for frame is the selected frame; the default for window is the selected window.
The value of minibuf specifies if the minibuffer window shall be included in the result list. If minibuf is
t, the result always includes the minibuffer window. If minibuf isnilor omitted, that includes the minibuffer window if it is active. If minibuf is neithernilnort, the result never includes the minibuffer window.
This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. See Displaying Buffers, for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use, but they employ heuristics in choosing or creating a window; use the functions described here when you need complete control.
This function makes window display buffer-or-name as its contents. It returns
nil. The default for window is the selected window. The argument buffer-or-name must specify a buffer or the name of an existing buffer.
set-window-bufferis the fundamental primitive for changing which buffer is displayed in a window, and all ways of doing that call this function.(set-window-buffer (selected-window) "foo") ⇒ nilNormally, displaying buffer-or-name in window resets the window's position, display margins, fringe widths, and scroll bar settings based on the local variables of that buffer. However, if keep-margins is non-
nil, display margins and fringe widths of window remain unchanged. See Fringes.
set-window-buffersignals an error when window is strongly dedicated to its buffer (see Dedicated Windows) and does not already display buffer-or-name.Note that this function runs
window-scroll-functionsbefore runningwindow-configuration-change-hook.
This buffer-local variable records the number of times a buffer has been displayed in a window. It is incremented each time
set-window-bufferis called for the buffer.
This function returns the buffer that window is displaying. The default for window is the selected window.
(window-buffer) ⇒ #<buffer windows.texi>
This function returns a window currently displaying buffer-or-name, or
nilif there is none. If there are several such windows, then the function returns the first one in the cyclic ordering of windows, starting from the selected window. See Cyclic Window Ordering.The argument BUFFER-OR-NAME may be a buffer or a buffer name and defaults to the current buffer. The optional argument all-frames specifies which windows to consider:
nilmeans consider windows on the selected frame.tmeans consider windows on all existing frames.visiblemeans consider windows on all visible frames.- 0 means consider windows on all visible or iconified frames.
- A frame means consider windows on that frame only.
Observe that the behavior of
get-buffer-windowmay differ from that ofnext-window(see Cyclic Window Ordering) when all-frames equalsnilor any value not listed here. Perhaps we will changeget-buffer-windowin the future to make it compatible with the other functions.
This function returns a list of all windows currently displaying buffer-or-name. The argument buffer-or-name may be a buffer or the name of an existing buffer and defaults to the current buffer.
The two remaining arguments work like the same-named arguments of
next-window; they are not like the optional arguments ofget-buffer-window.
This variable records the time at which a buffer was last made visible in a window. It is always local in each buffer; each time
set-window-bufferis called, it sets this variable to(current-time)in the specified buffer (see Time of Day). When a buffer is first created,buffer-display-timestarts out with the valuenil.
In this section we describe convenient functions that choose a window
automatically and use it to display a specified buffer. These functions
can also split an existing window in certain circumstances. We also
describe variables that parameterize the heuristics used for choosing a
window.
See Buffers and Windows, for
low-level primitives that give you more precise control. All of these
functions work by calling set-window-buffer.
Do not use the functions in this section in order to make a buffer
current so that a Lisp program can access or modify it; they are too
drastic for that purpose, since they change the display of buffers in
windows, which would be gratuitous and surprise the user. Instead, use
set-buffer and save-current-buffer (see Current Buffer), which designate buffers as current for programmed access
without affecting the display of buffers in windows.
This function makes buffer-or-name the current buffer, and also displays the buffer in the selected window. This means that a human can see the buffer and subsequent keyboard commands will apply to it. Contrast this with
set-buffer, which makes buffer-or-name the current buffer but does not display it in the selected window; see Current Buffer.If buffer-or-name is
nil,switch-to-bufferchooses a buffer usingother-buffer. If buffer-or-name is a string that does not identify an existing buffer, then a new buffer by that name is created. The major mode for the new buffer is set according to the variablemajor-mode; see Auto Major Mode.When the selected window is the minibuffer window or is strongly dedicated to its buffer (see Dedicated Windows), this function calls
pop-to-buffer(see below) to display the buffer in some other window.Normally the specified buffer is put at the front of the buffer list (both the selected frame's buffer list and the frame-independent buffer list). This affects the operation of
other-buffer. However, if norecord is non-nil, this is not done. See The Buffer List.The
switch-to-bufferfunction is often used interactively, as the binding of C-x b. It is also used frequently in programs. It returns the buffer that it switched to.
The next two functions are similar to switch-to-buffer, except
for the described features.
This function makes the buffer specified by buffer-or-name current and displays it in a window not currently selected, using the function
pop-to-buffer(see below).The currently selected window is absolutely never used to do the job. If the selected window already displays buffer-or-name, then it continues to do so, but another window is nonetheless found to display it in as well.
This function updates the buffer list just like
switch-to-bufferunless norecord is non-nil.
This command makes buffer-or-name the current buffer and switches to it in some window, preferably not the window previously selected. The “popped-to” window becomes the selected window. Its frame is given the X server's focus, if possible; see Input Focus. The return value is the buffer that was switched to.
If buffer-or-name is
nil, that means to choose some other buffer, but you don't specify which. If buffer-or-name is a string that does not name an existing buffer, a buffer by that name is created. The major mode for the new buffer is set according to the variablemajor-mode. See Auto Major Mode.If either of the variables
display-buffer-reuse-framesorpop-up-framesis non-nil,pop-to-bufferlooks for a window in any visible frame already displaying the buffer; if there is one, it selects and returns that window. If no such window exists andpop-up-framesis non-nil, it creates a new frame and displays the buffer in it. Otherwise,pop-to-bufferoperates entirely within the selected frame. (If the selected frame has just a minibuffer,pop-to-bufferoperates within the most recently selected frame that was not just a minibuffer.)If the variable
pop-up-windowsis non-nil, windows may be split to create a new window that is different from the original window. For details, see Choosing Window.If other-window is non-
nil,pop-to-bufferfinds or creates another window even if buffer-or-name is already visible in the selected window. Thus buffer-or-name could end up displayed in two windows. On the other hand, if buffer-or-name is already displayed in the selected window and other-window isnil, then the selected window is considered sufficient for displaying buffer-or-name, so that nothing needs to be done.All the variables that affect
display-bufferaffectpop-to-bufferas well. See Choosing Window.This function updates the buffer list just like
switch-to-bufferunless norecord is non-nil.
This function replaces buffer-or-name in all windows displaying it with some other buffer. It uses
other-bufferto choose the other buffer. In the usual applications of this function, you don't care which other buffer is used; you just want to make sure that buffer-or-name is no longer displayed.The argument buffer-or-name may be a buffer or the name of an existing buffer and defaults to the current buffer.
If a window displaying buffer-or-name is dedicated (see Dedicated Windows), and is not the only window on its frame, that window is deleted. If that window is the only window on its frame and there are other frames left, the window's frame is deleted too. If there are no other frames left, some other buffer is displayed in that window.
This function returns
nil.
This section describes the basic facility that chooses a window to
display a buffer in—display-buffer. Higher-level functions and
commands, like switch-to-buffer and pop-to-buffer, use this
subroutine. Here we describe how to use display-buffer and how
to customize it.
This command makes buffer-or-name appear in some window, but it does not select that window and does not make the buffer specified by buffer-or-name current. The identity of the selected window is unaltered by this function. The argument buffer-or-name must be a buffer or the name of an existing buffer.
not-this-window non-
nilmeans to display the specified buffer in a window other than the selected one, even if it is already displayed in the selected window. This can cause the buffer to appear in two windows at once. Otherwise, if buffer-or-name is already being displayed in any window, that is good enough, so this function does nothing.
display-bufferreturns the window chosen to display buffer-or-name.If the optional argument frame is non-
nil, it specifies which frames to check when deciding whether the buffer is already displayed. If the buffer is already displayed in some window on one of these frames,display-buffersimply returns that window. Here are the possible values of frame:
nilmeans consider windows on the selected frame. (Actually, the last non-minibuffer frame.)tmeans consider windows on all frames.visiblemeans consider windows on all visible frames.- 0 means consider windows on all visible or iconified frames.
- A frame means consider windows on that frame only.
Precisely how
display-bufferfinds or creates a window depends on the variables described below.
If this variable is non-
nil,display-buffersearches visible and iconified frames for a window displaying buffer-or-name. If there is such a window,display-buffermakes that window's frame visible and raises it if necessary, and returns the window. If there is no such window ordisplay-buffer-reuse-framesisnil, the behavior ofdisplay-bufferis determined by the variables described next.
This variable specifies whether
display-bufferis allowed to split (see Splitting Windows) an existing window. If this variable is non-nil,display-buffertries to split the largest or least recently used window on the selected frame. (If the selected frame is a minibuffer-only frame,display-buffertries to split a window on another frame instead.) If this variable isnilor the variablepop-up-frames(see below) is non-nil,display-bufferdoes not split any window.
This variable must specify a function with one argument, which is a window. The
display-bufferroutines will call this function with one or more candidate windows when they look for a window to split. The function is expected to split that window and return the new window. If the function returnsnil, this means that the argument window cannot (or shall not) be split.The default value of
split-window-preferred-functionis the functionsplit-window-sensiblydescribed below. If you customize this option, bear in mind that thedisplay-bufferroutines may call your function up to two times when trying to split a window. The argument of the first call is the largest window on the chosen frame (as returned byget-largest-window). If that call fails to return a live window, your function is called a second time with the least recently used window on that frame (as returned byget-lru-window).The function specified by this option may try to split any other window instead of the argument window. Note that the window selected at the time
display-bufferwas invoked is still selected when your function is called. Hence, you can split the selected window (instead of the largest or least recently used one) by simply ignoring the window argument in the body of your function. You can even choose to not split any window as long as the return value of your function specifies a live window ornil, but you are not encouraged to do so unconditionally. If you wantdisplay-bufferto never split any windows, setpop-up-windowstonil.
This function takes a window as argument and tries to split that window in a suitable way. The two variables described next are useful for tuning the behavior of this function.
This variable specifies whether
split-window-sensiblymay split windows vertically. If it is an integer,split-window-sensiblytries to vertically split a window only if it has at least this many lines. If the window has less lines, splitting fails, or the value of this variable isnil,split-window-sensiblywill try to split the window horizontally, subject to restrictions ofsplit-width-threshold(see below). If splitting horizontally fails too and the window is the only window on its frame,split-window-sensiblywill try to split the window vertically disregarding the value ofsplit-height-threshold. If this fails as well,split-window-sensiblyreturnsnil.
split-window-sensiblydoes not split vertically a window whose height is fixed (see Resizing Windows). Also, it vertically splits a window only if the space taken up by that window can accommodate two windows one above the other that are both at leastwindow-min-heightlines tall. Moreover, if the window that shall be split has a mode line,split-window-sensiblydoes not split the window unless the new window can accomodate a mode line too.
This variable specifies whether
split-window-sensiblymay split windows horizontally. If it is an integer,split-window-sensiblytries to horizontally split a window only if it has at least this many columns. If it isnil,split-window-sensiblywill not split the window horizontally. (It still might split the window vertically, though, see above.)
split-window-sensiblydoes not split horizontally a window if that window's width is fixed (see Resizing Windows). Also, it horizontally splits a window only if the space that window takes up can accommodate two windows side by side that are both at leastwindow-min-widthcolumns wide.
This variable specifies whether
display-buffershould even out window heights if the buffer gets displayed in an existing window, above or beneath another window. Ifeven-window-heightsis non-nil, the default, window heights will be evened out. If either of the involved window has fixed height (see Resizing Windows) oreven-window-heightsisnil, the original window heights will be left alone.
This variable specifies whether
display-buffershould make new frames. If it is non-nil,display-bufferlooks for a window already displaying buffer-or-name on any visible or iconified frame. If it finds such a window, it makes that window's frame visible and raises it if necessary, and returns the window. Otherwise it makes a new frame, unless the variable's value isgraphic-onlyand the selected frame is not on a graphic display. See Frames, for more information.Note that the value of
pop-up-windowsdoes not matter ifpop-up-framesis non-nil. Ifpop-up-framesisnil, thendisplay-buffereither splits a window or reuses one.
This variable specifies how to make a new frame if
pop-up-framesis non-nil.The value of this variable must be a function of no arguments. When
display-buffermakes a new frame, it does so by calling that function, which should return a frame. The default value of this variable is a function that creates a frame using the parameters specified bypop-up-frame-alistdescribed next.
This variable holds an alist specifying frame parameters used by the default value of
pop-up-frame-functionfor making new frames. See Frame Parameters, for more information about frame parameters.
A list of buffer names identifying buffers that should be displayed specially. If the name of buffer-or-name is in this list,
display-bufferhandles the buffer specially. By default, special display means to give the buffer a dedicated frame.If an element is a list, instead of a string, then the car of that list is the buffer name, and the rest of that list says how to create the frame. There are two possibilities for the rest of that list (its cdr): It can be an alist, specifying frame parameters, or it can contain a function and arguments to give to it. (The function's first argument is always the buffer to be displayed; the arguments from the list come after that.)
For example:
(("myfile" (minibuffer) (menu-bar-lines . 0)))specifies to display a buffer named ‘myfile’ in a dedicated frame with specified
minibufferandmenu-bar-linesparameters.The list of frame parameters can also use the phony frame parameters
same-frameandsame-window. If the specified frame parameters include(same-window .value)and value is non-nil, that means to display the buffer in the current selected window. Otherwise, if they include(same-frame .value)and value is non-nil, that means to display the buffer in a new window in the currently selected frame.
A list of regular expressions specifying buffers that should be displayed specially. If the buffer's name matches any of the regular expressions in this list,
display-bufferhandles the buffer specially. By default, special display means to give the buffer a dedicated frame.If an element is a list, instead of a string, then the car of the list is the regular expression, and the rest of the list says how to create the frame. See
special-display-buffer-namesabove.
This function returns non-
nilif displaying a buffer named buffer-name withdisplay-bufferwould create a special frame. The value istif it would use the default frame parameters, or else the specified list of frame parameters.
This variable holds the function to call to display a buffer specially. It receives the buffer as an argument, and should return the window in which it is displayed. The default value of this variable is
special-display-popup-frame, see below.
This function tries to make buffer visible in a frame of its own. If buffer is already displayed in some window, it makes that window's frame visible and raises it. Otherwise, it creates a frame that is dedicated to buffer. The return value is the window used to display buffer.
If args is an alist, it specifies frame parameters for the new frame. If args is a list whose car is a symbol, then
(carargs)is called as a function to actually create and set up the frame; it is called with buffer as first argument, and(cdrargs)as additional arguments.This function always uses an existing window displaying buffer, whether or not it is in a frame of its own; but if you set up the above variables in your init file, before buffer was created, then presumably the window was previously made by this function.
This variable holds frame parameters for
special-display-popup-frameto use when it creates a frame.
A list of buffer names for buffers that should be displayed in the selected window. If the buffer's name is in this list,
display-bufferhandles the buffer by switching to it in the selected window.
A list of regular expressions that specify buffers that should be displayed in the selected window. If the buffer's name matches any of the regular expressions in this list,
display-bufferhandles the buffer by switching to it in the selected window.
This function returns
tif displaying a buffer named buffer-name withdisplay-bufferwould put it in the selected window.
This variable is the most flexible way to customize the behavior of
display-buffer. If it is non-nil, it should be a function thatdisplay-buffercalls to do the work. The function should accept two arguments, the first two arguments thatdisplay-bufferreceived. It should choose or create a window, display the specified buffer in it, and then return the window.This variable takes precedence over all the other options described above.
If all options described above fail to produce a suitable window,
display-buffer tries to reuse an existing window. As a last
resort, it will try to display buffer-or-name on a separate frame.
In that case, the value of pop-up-frames is disregarded.
Functions for displaying a buffer can be told to not use specific
windows by marking these windows as dedicated to their buffers.
display-buffer (see Choosing Window) never uses a dedicated
window for displaying another buffer in it. get-lru-window and
get-largest-window (see Selecting Windows) do not consider
dedicated windows as candidates when their dedicated argument is
non-nil. The behavior of set-window-buffer
(see Buffers and Windows) with respect to dedicated windows is
slightly different, see below.
When delete-windows-on (see Deleting Windows) wants to delete
a dedicated window and that window is the only window on its frame, it
deletes the window's frame too, provided there are other frames left.
replace-buffer-in-windows (see Displaying Buffers) tries to
delete all dedicated windows showing its buffer argument. When such a
window is the only window on its frame, that frame is deleted, provided
there are other frames left. If there are no more frames left, some
other buffer is displayed in the window, and the window is marked as
non-dedicated.
When you kill a buffer (see Killing Buffers) displayed in a
dedicated window, any such window usually gets deleted too, since
kill-buffer calls replace-buffer-in-windows for cleaning
up windows. Burying a buffer (see The Buffer List) deletes the
selected window if it is dedicated to that buffer. If, however, that
window is the only window on its frame, bury-buffer displays
another buffer in it and iconifies the frame.
This function returns non-
nilif window is dedicated to its buffer andnilotherwise. More precisely, the return value is the value assigned by the last call ofset-window-dedicated-pfor window ornilif that function was never called with window as its argument. The default for window is the selected window.
This function marks window as dedicated to its buffer if flag is non-
nil, and non-dedicated otherwise.As a special case, if flag is
t, window becomes strongly dedicated to its buffer.set-window-buffersignals an error when the window it acts upon is strongly dedicated to its buffer and does not already display the buffer it is asked to display. Other functions do not treattdifferently from any non-nilvalue.
Each window has its own value of point (see Point), independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.
As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.
This function returns the current position of point in window. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected. The default for window is the selected window.
When window is the selected window and its buffer is also the current buffer, the value returned is the same as point in that buffer. Strictly speaking, it would be more correct to return the “top-level” value of point, outside of any
save-excursionforms. But that value is hard to find.
This function positions point in window at position position in window's buffer. It returns position.
If window is selected, and its buffer is current, this simply does
goto-char.
This variable specifies the marker insertion type (see Marker Insertion Types) of
window-point. The default isnil, sowindow-pointwill stay behind text inserted there.
Each window maintains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
After switching windows or buffers, and in some other cases, if the window start is in the middle of a line, Emacs adjusts the window start to the start of a line. This prevents certain operations from leaving the window start at a meaningless point within a line. This feature may interfere with testing some Lisp code by executing it using the commands of Lisp mode, because they trigger this readjustment. To test such code, put it into a command and bind the command to a key.
This function returns the display-start position of window window. If window is
nil, the selected window is used. For example,(window-start) ⇒ 7058When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or to
point-minif the buffer doesn't have any.Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)—to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay.
For a realistic example of using
window-start, see the description ofcount-lines. See Definition of count-lines.
This function returns the position where display of its buffer ends in window. The default for window is the selected window.
Simply changing the buffer text or moving point does not update the value that
window-endreturns. The value is updated only when Emacs redisplays and redisplay completes without being preempted.If the last redisplay of window was preempted, and did not finish, Emacs does not know the position of the end of display in that window. In that case, this function returns
nil.If update is non-
nil,window-endalways returns an up-to-date value for where display ends, based on the currentwindow-startvalue. If a previously saved value of that position is still valid,window-endreturns that value; otherwise it computes the correct value by scanning the buffer text.Even if update is non-
nil,window-enddoes not attempt to scroll the display if point has moved off the screen, the way real redisplay would do. It does not alter thewindow-startvalue. In effect, it reports where the displayed text will end if scrolling is not required.
This function sets the display-start position of window to position in window's buffer. It returns position.
The display routines insist that the position of point be visible when a buffer is displayed. Normally, they change the display-start position (that is, scroll the window) whenever necessary to make point visible. However, if you specify the start position with this function using
nilfor noforce, it means you want display to start at position even if that would put the location of point off the screen. If this does place point off screen, the display routines move point to the left margin on the middle line in the window.For example, if point is 1 and you set the start of the window to 37, the start of the next line, point will be “above” the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what ‘foo’ looks like before executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (save-excursion (goto-char 1) (forward-line 1) (point))) ⇒ 37 ;; Here is what ‘foo’ looks like after executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- 2 3 -!-4 5 6 ---------- Buffer: foo ----------If noforce is non-
nil, and position would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus position is not used.
This function returns non-
nilif position is within the range of text currently visible on the screen in window. It returnsnilif position is scrolled vertically out of view. Locations that are partially obscured are not considered visible unless partially is non-nil. The argument position defaults to the current position of point in window; window, to the selected window. If position ist, that means to check the last visible position in window.The
pos-visible-in-window-pfunction considers only vertical scrolling. If position is out of view only because window has been scrolled horizontally,pos-visible-in-window-preturns non-nilanyway. See Horizontal Scrolling.If position is visible,
pos-visible-in-window-preturnstif partially isnil; if partially is non-nil, and the character following position is fully visible, it returns a list of the form(x y), where x and y are the pixel coordinates relative to the top left corner of the window; otherwise it returns an extended list of the form(x y rtop rbot rowh vpos), where rtop and rbot specify the number of off-window pixels at the top and bottom of the row at position, rowh specifies the visible height of that row, and vpos specifies the vertical position (zero-based row number) of that row.Here is an example:
;; If point is off the screen now, recenter it now. (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0))
This function returns the height of text line line in window. If line is one of
header-lineormode-line,window-line-heightreturns information about the corresponding line of the window. Otherwise, line is a text line number starting from 0. A negative number counts from the end of the window. The default for line is the current line in window; the default for window is the selected window.If the display is not up to date,
window-line-heightreturnsnil. In that case,pos-visible-in-window-pmay be used to obtain related information.If there is no line corresponding to the specified line,
window-line-heightreturnsnil. Otherwise, it returns a list(height vpos ypos offbot), where height is the height in pixels of the visible part of the line, vpos and ypos are the vertical position in lines and pixels of the line relative to the top of the first text line, and offbot is the number of off-window pixels at the bottom of the text line. If there are off-window pixels at the top of the (first) text line, ypos is negative.
Textual scrolling means moving the text up or down through a
window. It works by changing the value of the window's display-start
location. It may also change the value of window-point to keep
point on the screen.
Textual scrolling was formerly called “vertical scrolling,” but we changed its name to distinguish it from the new vertical fractional scrolling feature (see Vertical Scrolling).
In the commands scroll-up and scroll-down, the directions
“up” and “down” refer to the motion of the text in the buffer at which
you are looking through the window. Imagine that the text is
written on a long roll of paper and that the scrolling commands move the
paper up and down. Thus, if you are looking at text in the middle of a
buffer and repeatedly call scroll-down, you will eventually see
the beginning of the buffer.
Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then “down” commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view.
The textual scrolling functions (aside from
scroll-other-window) have unpredictable results if the current
buffer is different from the buffer that is displayed in the selected
window. See Current Buffer.
If the window contains a row which is taller than the height of the
window (for example in the presence of a large image), the scroll
functions will adjust the window's vertical scroll position to scroll
the partially visible row. To disable this feature, Lisp code may bind
the variable auto-window-vscroll to nil (see Vertical Scrolling).
This function scrolls the text in the selected window upward count lines. If count is negative, scrolling is actually downward.
If count is
nil(or omitted), then the length of scroll isnext-screen-context-lineslines less than the usable height of the window (not counting its mode line).
scroll-upreturnsnil, unless it gets an error because it can't scroll any further.
This function scrolls the text in the selected window downward count lines. If count is negative, scrolling is actually upward.
If count is omitted or
nil, then the length of the scroll isnext-screen-context-lineslines less than the usable height of the window (not counting its mode line).
scroll-downreturnsnil, unless it gets an error because it can't scroll any further.
This function scrolls the text in another window upward count lines. Negative values of count, or
nil, are handled as inscroll-up.You can specify which buffer to scroll by setting the variable
other-window-scroll-bufferto a buffer. If that buffer isn't already displayed,scroll-other-windowdisplays it in some window.When the selected window is the minibuffer, the next window is normally the one at the top left corner. You can specify a different window to scroll, when the minibuffer is selected, by setting the variable
minibuffer-scroll-window. This variable has no effect when any other window is selected. When it is non-niland the minibuffer is selected, it takes precedence overother-window-scroll-buffer. See Definition of minibuffer-scroll-window.When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case,
scroll-other-windowattempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message ‘Beginning of buffer’.
If this variable is non-
nil, it tellsscroll-other-windowwhich buffer's window to scroll.
This option specifies the size of the scroll margin—a minimum number of lines between point and the top or bottom of a window. Whenever point gets within this many lines of the top or bottom of the window, redisplay scrolls the text automatically (if possible) to move point out of the margin, closer to the center of the window.
This variable controls how scrolling is done automatically when point moves off the screen (or into the scroll margin). If the value is a positive integer n, then redisplay scrolls the text up to n lines in either direction, if that will bring point back into proper view. This behavior is called conservative scrolling. Otherwise, scrolling happens in the usual way, under the control of other variables such as
scroll-up-aggressivelyandscroll-down-aggressively.The default value is zero, which means that conservative scrolling never happens.
The value of this variable should be either
nilor a fraction f between 0 and 1. If it is a fraction, that specifies where on the screen to put point when scrolling down. More precisely, when a window scrolls down because point is above the window start, the new start position is chosen to put point f part of the window height from the top. The larger f, the more aggressive the scrolling.A value of
nilis equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion.
Likewise, for scrolling up. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with
scroll-up-aggressively, a larger value scrolls more aggressively.
This variable is an older variant of
scroll-conservatively. The difference is that if its value is n, that permits scrolling only by precisely n lines, not a smaller number. This feature does not work withscroll-margin. The default value is zero.
If this option is
t, scrolling which would move the current point position out of the window chooses the new position of point so that the vertical position of the cursor is unchanged, if possible.If it is non-
niland nott, then the scrolling functions always preserve the vertical position of point, if possible.
The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example,
scroll-upwith an argument ofnilscrolls so that this many lines at the bottom of the window appear instead at the top. The default value is2.
This function scrolls the text in the selected window so that point is displayed at a specified vertical position within the window. It does not “move point” with respect to the text.
If count is a nonnegative number, that puts the line containing point count lines down from the top of the window. If count is a negative number, then it counts upward from the bottom of the window, so that −1 stands for the last usable line in the window. If count is a non-
nillist, then it stands for the line in the middle of the window.If count is
nil,recenterputs the line containing point in the middle of the window, then clears and redisplays the entire selected frame.When
recenteris called interactively, count is the raw prefix argument. Thus, typing C-u as the prefix sets the count to a non-nillist, while typing C-u 4 sets count to 4, which positions the current line four lines from the top.With an argument of zero,
recenterpositions the current line at the top of the window. This action is so handy that some people make a separate key binding to do this. For example,(defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key [kp-multiply] 'line-to-top-of-window)
Vertical fractional scrolling means shifting text in a window up or down by a specified multiple or fraction of a line. Each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to raise the contents of the window. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero.
The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents are scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height.
What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image.
This function returns the current vertical scroll position of window. The default for window is the selected window. If pixels-p is non-
nil, the return value is measured in pixels, rather than in units of the normal line height.(window-vscroll) ⇒ 0
This function sets window's vertical scroll position to lines. If window is
nil, the selected window is used. The argument lines should be zero or positive; if not, it is taken as zero.The actual vertical scroll position must always correspond to an integral number of pixels, so the value you specify is rounded accordingly.
The return value is the result of this rounding.
(set-window-vscroll (selected-window) 1.2) ⇒ 1.13If pixels-p is non-
nil, lines specifies a number of pixels. In this case, the return value is lines.
If this variable is non-
nil, the line-move, scroll-up, and scroll-down functions will automatically modify the vertical scroll position to scroll through display rows that are taller than the height of the window, for example in the presence of large images.
Horizontal scrolling means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a horizontal scroll position, which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero.
The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line.
Because we read from side to side in the “inner loop,” and from top to bottom in the “outer loop,” the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of each line to go off screen.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.
If auto-hscroll-mode is set, redisplay automatically alters
the horizontal scrolling of a window as necessary to ensure that point
is always visible. However, you can still set the horizontal
scrolling value explicitly. The value you specify serves as a lower
bound for automatic scrolling, i.e. automatic scrolling will not
scroll a window to a column less than the specified one.
This function scrolls the selected window count columns to the left (or to the right if count is negative). The default for count is the window width, minus 2.
The return value is the total amount of leftward horizontal scrolling in effect after the change—just like the value returned by
window-hscroll(below).Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect.
If set-minimum is non-
nil, the new scroll amount becomes the lower bound for automatic scrolling; that is, automatic scrolling will not scroll a window to a column less than the value returned by this function. Interactive calls pass non-nilfor set-minimum.
This function scrolls the selected window count columns to the right (or to the left if count is negative). The default for count is the window width, minus 2. Aside from the direction of scrolling, this works just like
scroll-left.
This function returns the total leftward horizontal scrolling of window—the number of columns by which the text in window is scrolled left past the left margin. The default for window is the selected window.
The return value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).
(window-hscroll) ⇒ 0 (scroll-left 5) ⇒ 5 (window-hscroll) ⇒ 5
This function sets horizontal scrolling of window. The value of columns specifies the amount of scrolling, in terms of columns from the left margin. The argument columns should be zero or positive; if not, it is taken as zero. Fractional values of columns are not supported at present.
Note that
set-window-hscrollmay appear not to work if you test it by evaluating a call with M-: in a simple way. What happens is that the function sets the horizontal scroll value and returns, but then redisplay adjusts the horizontal scrolling to make point visible, and this overrides what the function did. You can observe the function's effect if you call it while point is sufficiently far from the left margin that it will remain visible.The value returned is columns.
(set-window-hscroll (selected-window) 10) ⇒ 10
Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:
(defun hscroll-on-screen (window position)
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window)))))
An Emacs window is rectangular, and its size information consists of the height (the number of lines) and the width (the number of character positions in each line). The mode line is included in the height. But the width does not count the scroll bar or the column of ‘|’ characters that separates side-by-side windows.
The following three functions return size information about a window:
This function returns the number of lines in window (by default the selected window), including any mode line and header line. The result is almost always less than the value of
frame-heightfor the associated frame, because the latter also includes any echo area. Depending on the toolkit in use, the frame height can also include the menu bar and tool bar (see Size and Position). Therefore in general it is not straightforward to compare window and frame heights (seewindow-full-height-pbelow).(window-height) ⇒ 23 (split-window-vertically) ⇒ #<window 4 on windows.texi> (window-height) ⇒ 11
Like
window-heightbut the value does not include the mode line (if any) or the header line (if any).
This function returns non-
nilif window is as tall as the frame that contains it. The default for window is the selected window.
This function returns the number of columns in window. The default for window is the selected window.
The return value does not include the window's scroll bar or the column of ‘|’ characters that separates side-by-side windows. Moreover, the return value does not include the space used for displaying fringes and margins. Hence you cannot, in general, compare the return values of
window-widthandframe-widthfor equality to determine whether a window is a wide as the containing frame. Use the functionwindow-full-width-p, see below, instead.(window-width) ⇒ 80
This function returns non-
nilif window is as wide as the frame that contains it; otherwisenil. The default for window is the selected window.
This function returns a list of the edge coordinates of window. The default for window is the selected window.
The order of the list is
(left top right bottom), all elements relative to 0, 0 at the top left corner of the frame. The element right of the value is one more than the rightmost column used by window, and bottom is one more than the bottommost row used by window and its mode-line.The edges include the space used by the window's scroll bar, display margins, fringes, header line, and mode line, if it has them. Also, if the window has a neighbor on the right, its right edge value includes the width of the separator line between the window and that neighbor. Since the width of the window does not include this separator, the width does not usually equal the difference between the right and left edges.
This is similar to
window-edges, but the edge values it returns include only the text area of the window. They do not include the header line, mode line, scroll bar or vertical separator, fringes, or display margins.
Here are the results obtained on a typical 24-line terminal with just one window, with menu bar enabled:
(window-edges (selected-window))
⇒ (0 1 80 23)
(window-inside-edges (selected-window))
⇒ (0 1 80 22)
The bottom edge is at line 23 because the last line is the echo area. The bottom inside edge is at line 22, which is the window's mode line.
If window is at the upper left corner of its frame, and there is
no menu bar, then bottom returned by window-edges is the
same as the value of (window-height), right is almost the
same as the value of (window-width), and top and
left are zero. For example, the edges of the following window
are ‘0 0 8 5’. Assuming that the frame has more than 8
columns, the last column of the window (column 7) holds a border
rather than text. The last row (row 4) holds the mode line, shown
here with ‘xxxxxxxxx’.
0
_______
0 | |
| |
| |
| |
xxxxxxxxx 4
7
In the following example, let's suppose that the frame is 7 columns wide. Then the edges of the left window are ‘0 0 4 3’ and the edges of the right window are ‘4 0 7 3’. The inside edges of the left window are ‘0 0 3 2’, and the inside edges of the right window are ‘4 0 7 2’,
___ ___
| | |
| | |
xxxxxxxxx
0 34 7
This function is like
window-edgesexcept that, on a graphical display, the edge values are measured in pixels instead of in character lines and columns.
This function is like
window-inside-edgesexcept that, on a graphical display, the edge values are measured in pixels instead of in character lines and columns.
The window size functions fall into two classes: high-level commands that change the size of windows and low-level functions that access window size. Emacs does not permit overlapping windows or gaps between windows, so resizing a window always affects at least one other window.
This function makes the selected window size lines taller by stealing lines from windows above or below. In a first round, it takes lines from one window at a time until that window is
window-min-heightlines tall, then takes from another. If, at the end of the first round, the selected window is still not tall enough,enlarge-windowstarts a second round, where it deletes windows above or below the selected one.If horizontal is non-
nil, this function makes the window size columns wider, stealing columns instead of lines. If a window from which columns are stolen shrinks belowwindow-min-widthcolumns, that window disappears.If the requested size would exceed that of the window's frame, then the function makes the window occupy the entire height (or width) of the frame.
If there are various other windows from which lines or columns can be stolen, and some of them specify fixed size (using
window-size-fixed, see below), they are left untouched while other windows are “robbed.” If it would be necessary to alter the size of a fixed-size window,enlarge-windowgets an error instead.If size is negative, this function shrinks the selected window by −size lines or columns. If that makes the window smaller than the minimum size (
window-min-heightandwindow-min-width), thenenlarge-windowdeletes the window.
enlarge-windowreturnsnil.
This function makes the selected window columns wider. It could be defined as follows:
(defun enlarge-window-horizontally (columns) (interactive "p") (enlarge-window columns t))
This function is like
enlarge-windowbut negates the argument size, making the selected window smaller by giving lines (or columns) to the other windows. If the window shrinks belowwindow-min-heightorwindow-min-width, then it disappears.If size is negative, the window is enlarged by −size lines or columns.
This function makes the selected window columns narrower. It could be defined as follows:
(defun shrink-window-horizontally (columns) (interactive "p") (shrink-window columns t))
This function makes the selected window delta lines taller or delta columns wider, by moving the bottom or right edge. This function does not delete other windows; if it cannot make the requested size adjustment, it signals an error. On success, this function returns
nil.
This command makes window the right height to display its contents exactly. The default for window is the selected window.
The optional argument max-height specifies the maximum height the window is allowed to be;
nilmeans use the maximum permissible height of a window on window's frame. The optional argument min-height specifies the minimum height for the window;nilmeans usewindow-min-height. All these height values include the mode line and/or header line.This function can delete windows when their height shrinks below min-height. It returns non-
nilif it orderly resized window, andnilotherwise.
This command shrinks window vertically to be as small as possible while still showing the full contents of its buffer—but not less than
window-min-heightlines. The default for window is the selected window.However, this command does nothing if the window is already too small to display the whole text of the buffer, or if part of the contents are currently scrolled off screen, or if the window is not the full width of its frame, or if the window is the only window in its frame.
This command returns non-
nilif it actually shrank the window andnilotherwise.
If this variable is non-
nil, in a given buffer, then the size of any window displaying that buffer remains fixed unless you either explicitly change it or Emacs has no other choice.If the value is
height, then only the window's height is fixed; if the value iswidth, then only the window's width is fixed. Any other non-nilvalue fixes both the width and the height.This variable automatically becomes buffer-local when set.
Explicit size-change functions such as
enlarge-windowget an error if they would have to change a window size which is fixed. Therefore, when you want to change the size of such a window, you should bindwindow-size-fixedtonil, like this:(let ((window-size-fixed nil)) (enlarge-window 10))Deleting an adjacent window or changing the frame size may change the size of a fixed-size window, if there is no other alternative.
The following two variables constrain the window-structure-changing functions to a minimum height and width.
The value of this variable specifies how short a window may become before it is automatically deleted. Making a window smaller than
window-min-heightautomatically deletes it, and no window may be created shorter than this. The value is measured in line units. When the window wants a mode line and/or a header line, they are counted as one line each. The default value is4. A value less than1is ignored.
The value of this variable specifies how narrow a window may become before it is automatically deleted. Making a window smaller than
window-min-widthautomatically deletes it, and no window may be created narrower than this. The value is measured in characters and includes any fringes or the scroll bar. The default value is10. A value less than2is ignored.
Emacs provides two functions to balance windows, that is, to even out the sizes of windows on the same frame. The minibuffer window and fixed-size windows are not resized by these functions.
This function balances windows in a way that gives more space to full-width and/or full-height windows. If window-or-frame specifies a frame, it balances all windows on that frame. If window-or-frame specifies a window, it balances this window and its “siblings” only. Think of a sibling as the other (original or new) window with respect to the present one, involved in the process of splitting; see Splitting Windows. Since a sibling may have been split again, a window can have more than one sibling.
This function attempts to give all windows on the selected frame approximately the same share of the screen area. This means that full-width or full-height windows are not given more space than other windows.
This section describes how to relate screen coordinates to windows.
This function returns the window containing the specified cursor position in the frame frame. The coordinates x and y are measured in characters and count from the top left corner of the frame. If they are out of range,
window-atreturnsnil.If you omit frame, the selected frame is used.
This function checks whether a particular frame position falls within the window window.
The argument coordinates is a cons cell of the form
(x.y). The coordinates x and y are measured in characters, and count from the top left corner of the screen or frame.The value returned by
coordinates-in-window-pis non-nilif the coordinates are inside window. The value also indicates what part of the window the position is in, as follows:
(relx.rely)- The coordinates are inside window. The numbers relx and rely are the equivalent window-relative coordinates for the specified position, counting from 0 at the top left corner of the window.
mode-line- The coordinates are in the mode line of window.
header-line- The coordinates are in the header line of window.
vertical-line- The coordinates are in the vertical line between window and its neighbor to the right. This value occurs only if the window doesn't have a scroll bar; positions in a scroll bar are considered outside the window for these purposes.
left-fringeright-fringe- The coordinates are in the left or right fringe of the window.
left-marginright-margin- The coordinates are in the left or right margin of the window.
nil- The coordinates are not in any part of window.
The function
coordinates-in-window-pdoes not require a frame as argument because it always uses the frame that window is on.
A window tree specifies the layout, size, and relationship between all windows in one frame.
This function returns the window tree for frame frame. If frame is omitted, the selected frame is used.
The return value is a list of the form
(root mini), where root represents the window tree of the frame's root window, and mini is the frame's minibuffer window.If the root window is not split, root is the root window itself. Otherwise, root is a list
(dir edges w1 w2...)where dir isnilfor a horizontal split, andtfor a vertical split, edges gives the combined size and position of the subwindows in the split, and the rest of the elements are the subwindows in the split. Each of the subwindows may again be a window or a list representing a window split, and so on. The edges element is a list(left top right bottom)similar to the value returned bywindow-edges.
A window configuration records the entire layout of one
frame—all windows, their sizes, which buffers they contain, how those
buffers are scrolled, and their values of point and the mark; also their
fringes, margins, and scroll bar settings. It also includes the value
of minibuffer-scroll-window. As a special exception, the window
configuration does not record the value of point in the selected window
for the current buffer. Also, the window configuration does not record
the values of window parameters; see Window Parameters.
You can bring back an entire frame layout by restoring a previously saved window configuration. If you want to record the layout of all frames instead of just one, use a frame configuration instead of a window configuration; see Frame Configurations.
This function returns a new object representing frame's current window configuration. The default for frame is the selected frame.
This function restores the configuration of windows and buffers as specified by configuration, for the frame that configuration was created for.
The argument configuration must be a value that was previously returned by
current-window-configuration. The configuration is restored in the frame from which configuration was made, whether that frame is selected or not. This always counts as a window size change and triggers execution of thewindow-size-change-functions(see Window Hooks), becauseset-window-configurationdoesn't know how to tell whether the new configuration actually differs from the old one.If the frame which configuration was saved from is dead, all this function does is restore the three variables
window-min-height,window-min-widthandminibuffer-scroll-window. In this case, the function returnsnil. Otherwise, it returnst.Here is a way of using this function to get the same effect as
save-window-excursion:(let ((config (current-window-configuration))) (unwind-protect (progn (split-window-vertically nil) ...) (set-window-configuration config)))
This special form records the window configuration, executes forms in sequence, then restores the earlier window configuration. The window configuration includes, for each window, the value of point and the portion of the buffer that is visible. It also includes the choice of selected window. However, it does not include the value of point in the current buffer; use
save-excursionalso, if you wish to preserve that.Don't use this construct when
save-selected-windowis sufficient.Exit from
save-window-excursionalways triggers execution ofwindow-size-change-functions. (It doesn't know how to tell whether the restored configuration actually differs from the one in effect at the end of the forms.)The return value is the value of the final form in forms. For example:
(split-window) ⇒ #<window 25 on control.texi> (setq w (selected-window)) ⇒ #<window 19 on control.texi> (save-window-excursion (delete-other-windows w) (switch-to-buffer "foo") 'do-something) ⇒ do-something ;; The screen is now split again.
This function returns
tif object is a window configuration.
This function compares two window configurations as regards the structure of windows, but ignores the values of point and mark and the saved scrolling positions—it can return
teven if those aspects differ.The function
equalcan also compare two window configurations; it regards configurations as unequal if they differ in any respect, even a saved point or mark.
This function returns the frame for which the window configuration config was made.
Other primitives to look inside of window configurations would make sense, but are not implemented because we did not need them. See the file winner.el for some more operations on windows configurations.
This sections describes how window parameters can be used to associate additional information with windows.
This function returns window's value for parameter. The default for window is the selected window. If window has no setting for parameter, this function returns
nil.
This function returns all parameters of window and their values. The default for window is the selected window. The return value is an association list of elements of the form
(parameter.value).
This function sets window's value of parameter to value and returns value. The default for window is the selected window.
Currently, window parameters are not saved in window configurations and
consequently not restored by set-window-configuration. Hence,
any change of a parameter introduced via set-window-parameter can
be undone only by invoking set-window-parameter for the same
parameter again. Since save-window-excursion relies on window
configurations (see Window Configurations), window parameters are
not saved and restored by that special form, either.
This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run window-scroll-functions; the last runs
window-size-change-functions.
This variable holds a list of functions that Emacs should call before redisplaying a window with scrolling. Displaying a different buffer in the window also runs these functions.
This variable is not a normal hook, because each function is called with two arguments: the window, and its new display-start position.
These functions must be careful in using
window-end(see Window Start and End); if you need an up-to-date value, you must use the update argument to ensure you get it.Warning: don't use this feature to alter the way the window is scrolled. It's not designed for that, and such use probably won't work.
This variable holds a list of functions to be called if the size of any window changes for any reason. The functions are called just once per redisplay, and just once for each frame on which size changes have occurred.
Each function receives the frame as its sole argument. There is no direct way to find out which windows on that frame have changed size, or precisely how. However, if a size-change function records, at each call, the existing windows and their sizes, it can also compare the present sizes and the previous sizes.
Creating or deleting windows counts as a size change, and therefore causes these functions to be called. Changing the frame size also counts, because it changes the sizes of the existing windows.
It is not a good idea to use
save-window-excursion(see Window Configurations) in these functions, because that always counts as a size change, and it would cause these functions to be called over and over. In most cases,save-selected-window(see Selecting Windows) is what you need here.
A normal hook that is run every time you change the window configuration of an existing frame. This includes splitting or deleting windows, changing the sizes of windows, or displaying a different buffer in a window.
The buffer-local part of this hook is run once per each window on the affected frame, with the relevant window selected and its buffer current. The global part is run once for the modified frame, with that frame selected.
In addition, you can use jit-lock-register to register a Font
Lock fontification function, which will be called whenever parts of a
buffer are (re)fontified because a window was scrolled or its size
changed. See Other Font Lock Variables.
A frame is a screen object that contains one or more Emacs windows (see Windows). It is the kind of object called a “window” in the terminology of graphical environments; but we can't call it a “window” here, because Emacs uses that word in a different way. In Emacs Lisp, a frame object is a Lisp object that represents a frame on the screen. See 框类型.
A frame initially contains a single main window and/or a minibuffer window; you can subdivide the main window vertically or horizontally into smaller windows. See Splitting Windows.
A terminal is a display device capable of displaying one or more Emacs frames. In Emacs Lisp, a terminal object is a Lisp object that represents a terminal. See 终端类型.
There are two classes of terminals: text-only terminals and graphical terminals. Text-only terminals are non-graphics-capable display devices, including “terminal emulators” such as xterm. On text-only terminals, each frame occupies the entire terminal screen; although you can create additional frames and switch between them, only one frame can be shown at any given time. We refer to frames on text-only terminals as terminal frames. Graphical terminals, on the other hand, are graphics-capable windowing systems, such as the X Window System. On a graphical terminal, Emacs can display multiple frames simultaneously. We refer to such frames as window frames.
On GNU and Unix systems, you can create additional frames on any available terminal, within a single Emacs session, regardless of whether Emacs was started on a text-only or graphical terminal. Emacs can display on both graphical and text-only terminals simultaneously. This comes in handy, for instance, when you connect to the same session from several remote locations. See Multiple Terminals.
This predicate returns a non-
nilvalue if object is a frame, andnilotherwise. For a frame, the value indicates which kind of display the frame uses:
x- The frame is displayed in an X window.
t- A terminal frame on a character display.
w32- The frame is displayed on MS-Windows 9X/NT.
ns- The frame is displayed on a GNUstep or Macintosh Cocoa display.
pc- The frame is displayed on an MS-DOS terminal.
This function returns the terminal object that displays frame. If frame is
nilor unspecified, it defaults to the selected frame.
This predicate returns a non-
nilvalue if object is a terminal that is alive (i.e. was not deleted), andnilotherwise. For live terminals, the return value indicates what kind of frames are displayed on that terminal; the list of possible values is the same as forframepabove.
To create a new frame, call the function make-frame.
This function creates and returns a new frame, displaying the current buffer.
The alist argument is an alist that specifies frame parameters for the new frame. See Frame Parameters. If you specify the
terminalparameter in alist, the new frame is created on that terminal. Otherwise, if you specify thewindow-systemframe parameter in alist, that determines whether the frame should be displayed on a text-only or graphical terminal. See Window Systems. If neither is specified, the new frame is created in the same terminal as the selected frame.Any parameters not mentioned in alist default to the values in the alist
default-frame-alist(see Initial Parameters); parameters not specified there default from the X resources or its equivalent on your operating system (see X Resources). After the frame is created, Emacs applies any parameters listed inframe-inherited-parameters(see below) and not present in the argument, taking the values from the frame that was selected whenmake-framewas called.This function itself does not make the new frame the selected frame. See Input Focus. The previously selected frame remains selected. On graphical terminals, however, the windowing system may select the new frame for its own reasons.
An abnormal hook run by
make-frameafter it creates the frame. Each function inafter-make-frame-functionsreceives one argument, the frame just created.
This variable specifies the list of frame parameters that a newly created frame inherits from the currently selected frame. For each parameter (a symbol) that is an element in the list and is not present in the argument to
make-frame, the function sets the value of that parameter in the created frame to its value in the selected frame.
Emacs represents each terminal, whether graphical or text-only, as a terminal object data type (see 终端类型). On GNU and Unix systems, Emacs can use multiple terminals simultaneously in each session. On other systems, it can only use a single terminal. Each terminal object has the following attributes:
terminal-live-p (i.e., x,
t, w32, ns, or pc). See Frames.
There is no primitive for creating terminal objects. Emacs creates
them as needed, such as when you call make-frame-on-display
(which is described below).
This function returns the file name of the device used by terminal. If terminal is omitted or
nil, it defaults to the selected frame's terminal. terminal can also be a frame, meaning that frame's terminal.
This function returns a terminal whose device name is given by device. If device is a string, it can be either the file name of a terminal device, or the name of an X display of the form ‘host:server.screen’. If device is a frame, this function returns that frame's terminal;
nilmeans the selected frame. Finally, if device is a terminal object that represents a live terminal, that terminal is returned. The function signals an error if its argument is none of the above.
This function deletes all frames on terminal and frees the resources used by it. It runs the abnormal hook
delete-terminal-functions, passing terminal as the argument to each function.If terminal is omitted or
nil, it defaults to the selected frame's terminal. terminal can also be a frame, meaning that frame's terminal.Normally, this function signals an error if you attempt to delete the sole active terminal, but if force is non-
nil, you are allowed to do so. Emacs automatically calls this function when the last frame on a terminal is deleted (see Deleting Frames).
An abnormal hook run by
delete-terminal. Each function receives one argument, the terminal argument passed todelete-terminal. Due to technical details, the functions may be called either just before the terminal is deleted, or just afterwards.
A few Lisp variables are terminal-local; that is, they have a
separate binding for each terminal. The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to. These variables include default-minibuffer-frame,
defining-kbd-macro, last-kbd-macro, and
system-key-alist. They are always terminal-local, and can
never be buffer-local (see Buffer-Local Variables).
On GNU and Unix systems, each X display is a separate graphical
terminal. When Emacs is started from within the X window system, it
uses the X display chosen with the DISPLAY environment
variable, or with the ‘--display’ option. See Initial Options. Emacs can connect to other X
displays via the command make-frame-on-display. Each X display
has its own selected frame and its own minibuffer windows; however,
only one of those frames is “the selected frame” at any given
moment (see Input Focus). Emacs can even connect to other
text-only terminals, by interacting with the emacsclient
program. See Emacs Server.
A single X server can handle more than one display. Each X display has a three-part name, ‘host:server.screen’. The first two parts, host and server, identify the X server; the third part, screen, identifies a screen number on that X server. When you use two or more screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard.
On some “multi-monitor” setups, a single X display outputs to more than one monitor. Currently, there is no way for Emacs to distinguish between the different physical monitors.
This function creates and returns a new frame on display, taking the other frame parameters from the alist parameters. display should be the name of an X display (a string).
Before creating the frame, this function ensures that Emacs is “set up” to display graphics. For instance, if Emacs has not processed X resources (e.g., if it was started on a text-only terminal), it does so at this time. In all other respects, this function behaves like
make-frame(see Creating Frames).
This function returns a list that indicates which X displays Emacs has a connection to. The elements of the list are strings, and each one is a display name.
This function opens a connection to the X display display, without creating a frame on that display. Normally, Emacs Lisp programs need not call this function, as
make-frame-on-displaycalls it automatically. The only reason for calling it is to check whether communication can be established with a given X display.The optional argument xrm-string, if not
nil, is a string of resource names and values, in the same format used in the .Xresources file. See X Resources. These values apply to all Emacs frames created on this display, overriding the resource values recorded in the X server. Here's an example of what this string might look like:"*BorderWidth: 3\n*InternalBorder: 2\n"If must-succeed is non-
nil, failure to open the connection terminates Emacs. Otherwise, it is an ordinary Lisp error.
This function closes the connection to display display. Before you can do this, you must first delete all the frames that were open on that display (see Deleting Frames).
A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses.
Frame parameters exist mostly for the sake of window systems. A
terminal frame has a few parameters, mostly for compatibility's sake;
only the height, width, name, title,
menu-bar-lines, buffer-list and buffer-predicate
parameters do something special. If the terminal supports colors, the
parameters foreground-color, background-color,
background-mode and display-type are also meaningful.
If the terminal supports frame transparency, the parameter
alpha is also meaningful.
You can use frame parameters to define frame-local bindings for variables. See Frame-Local Variables.
These functions let you read and change the parameter values of a frame.
This function returns the value of the parameter parameter (a symbol) of frame. If frame is
nil, it returns the selected frame's parameter. If frame has no setting for parameter, this function returnsnil.
The function
frame-parametersreturns an alist listing all the parameters of frame and their values. If frame isnilor omitted, this returns the selected frame's parameters
This function alters the parameters of frame frame based on the elements of alist. Each element of alist has the form
(parm.value), where parm is a symbol naming a parameter. If you don't mention a parameter in alist, its value doesn't change. If frame isnil, it defaults to the selected frame.You can use this function to define frame-local bindings for variables, see Frame-Local Variables.
This function sets the frame parameter parm to the specified value. If frame is
nil, it defaults to the selected frame.
This function alters the frame parameters of all existing frames according to alist, then modifies
default-frame-alist(and, if necessary,initial-frame-alist) to apply the same parameter values to frames that will be created henceforth.
You can specify the parameters for the initial startup frame
by setting initial-frame-alist in your init file (see Init File).
This variable's value is an alist of parameter values used when creating the initial window frame. You can set this variable to specify the appearance of the initial frame without altering subsequent frames. Each element has the form:
(parameter . value)Emacs creates the initial frame before it reads your init file. After reading that file, Emacs checks
initial-frame-alist, and applies the parameter settings in the altered value to the already created initial frame.If these settings affect the frame geometry and appearance, you'll see the frame appear with the wrong ones and then change to the specified ones. If that bothers you, you can specify the same geometry and appearance with X resources; those do take effect before the frame is created. See X Resources.
X resource settings typically apply to all frames. If you want to specify some X resources solely for the sake of the initial frame, and you don't want them to apply to subsequent frames, here's how to achieve this. Specify parameters in
default-frame-alistto override the X resources for subsequent frames; then, to prevent these from affecting the initial frame, specify the same parameters ininitial-frame-alistwith values that match the X resources.
If these parameters specify a separate minibuffer-only frame with
(minibuffer . nil), and you have not created one, Emacs creates
one for you.
This variable's value is an alist of parameter values used when creating an initial minibuffer-only frame. This is the minibuffer-only frame that Emacs creates if
initial-frame-alistspecifies a frame with no minibuffer.
This is an alist specifying default values of frame parameters for all Emacs frames—the first frame, and subsequent frames. When using the X Window System, you can get the same results by means of X resources in many cases.
Setting this variable does not affect existing frames.
Functions that display a buffer in a separate frame can override the default parameters by supplying their own parameters. See Definition of special-display-frame-alist.
If you use options that specify window appearance when you invoke Emacs,
they take effect by adding elements to default-frame-alist. One
exception is ‘-geometry’, which adds the specified position to
initial-frame-alist instead. See Command Line Arguments for Emacs Invocation.
Just what parameters a frame has depends on what display mechanism
it uses. This section describes the parameters that have special
meanings on some or all kinds of terminals. Of these, name,
title, height, width, buffer-list and
buffer-predicate provide meaningful information in terminal
frames, and tty-color-mode is meaningful only in
terminal frames.
These frame parameters give the most basic information about the
frame. title and name are meaningful on all terminals.
display"host:dpy.screen", just like the
DISPLAY environment variable.
display-typecolor, grayscale or
mono.
titlenil title, it appears in the window
system's title bar at the top of the frame, and also in the mode line
of windows in that frame if mode-line-frame-identification uses
‘%F’ (see %-Constructs). This is normally the case when
Emacs is not using a window system, and can only display one frame at
a time. See Frame Titles.
nametitle parameter is unspecified or nil. If
you don't specify a name, Emacs sets the frame name automatically
(see Frame Titles).
If you specify the frame name explicitly when you create the frame, the name is also used (instead of the name of the Emacs executable) when looking up X resources for the frame.
Position parameters' values are normally measured in pixels, but on text-only terminals they count characters or lines instead.
left(+ pos)(- pos)Some window managers ignore program-specified positions. If you want to
be sure the position you specify is not ignored, specify a
non-nil value for the user-position parameter as well.
topleft, except vertically instead of horizontally.
icon-leftIf you specify a value for this parameter, then you must also specify
a value for icon-top and vice versa. The window manager may
ignore these two parameters.
icon-topuser-positionleft and top parameters, use this parameter to say whether
the specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a program).
A non-nil value says the position was user-specified.
Window managers generally heed user-specified positions, and some heed
program-specified positions too. But many ignore program-specified
positions, placing the window in a default fashion or letting the user
place it with the mouse. Some window managers, including twm,
let the user specify whether to obey program-specified positions or
ignore them.
When you call make-frame, you should specify a non-nil
value for this parameter if the values of the left and top
parameters represent the user's stated preference; otherwise, use
nil.
Size parameters' values are normally measured in pixels, but on text-only terminals they count characters or lines instead.
heightframe-pixel-height; see Size and Position.)
widthframe-pixel-width; see Size and Position.)
user-sizeheight and width what
the user-position parameter (see above) does for the position
parameters top and left.
fullscreenfullwidth specifies that width shall be as wide as possible.
The value fullheight specifies that height shall be as tall as
possible. The value fullboth specifies that both the width and
the height shall be set to the size of the screen. The value
maximized specifies that the frame shall be maximized. The
difference between maximized and fullboth is that the
former still has window manager decorations while the latter really
covers the whole screen.
These frame parameters enable or disable various parts of the frame, or control their sizes.
border-widthinternal-border-widthvertical-scroll-barsleft,
right, and nil for no scroll bars.
scroll-bar-widthnil meaning to
use the default width.
left-fringeright-fringenil stands for
the standard fringe width, which is the width needed to display the
fringe bitmaps.
The combined fringe widths must add up to an integral number of
columns, so the actual default fringe widths for the frame may be
larger than the specified values. The extra width needed to reach an
acceptable total is distributed evenly between the left and right
fringe. However, you can force one fringe or the other to a precise
width by specifying that width as a negative integer. If both widths are
negative, only the left fringe gets the specified width.
menu-bar-linesnil means don't display a
menu bar. See Menu Bar. (The X toolkit and GTK allow at most one
menu bar line; they treat larger values as 1.)
tool-bar-linesnil
means don't display a tool bar. (GTK and Nextstep allow at most one
tool bar line; they treat larger values as 1.)
line-spacingThese frame parameters, meaningful on all kinds of terminals, deal with which buffers have been, or should, be displayed in the frame.
minibuffert means
yes, nil means no, only means this frame is just a
minibuffer. If the value is a minibuffer window (in some other
frame), the frame uses that minibuffer.
This frame parameter takes effect when the frame is created, and can
not be changed afterwards.
buffer-predicateother-buffer uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
nil. It calls the predicate with one argument, a buffer, once for
each buffer; if the predicate returns a non-nil value, it
considers that buffer.
buffer-listunsplittablenil, this frame's window is never split automatically.
These frame parameters, meaningful only on window system displays, interact with the window manager.
visibilitynil for invisible, t for visible, and icon for
iconified. See Visibility of Frames.
auto-raisenil means yes).
auto-lowernil means yes).
icon-typenil value specifies the default bitmap icon (a
picture of a gnu); nil specifies a text icon.
icon-namenil, the frame's title is used.
window-idouter-window-idwait-for-wmnil, tell Xt to wait for the window manager to confirm
geometry changes. Some window managers, including versions of Fvwm2
and KDE, fail to confirm, so Xt hangs. Set this to nil to
prevent hanging with those window managers.
stickynil, the frame is visible on all virtual desktops on systems
with virtual desktops.
This frame parameter controls the way the cursor looks.
cursor-typeboxhollownilbar(bar . width)hbar(hbar . height)The buffer-local variable cursor-type overrides the value of
the cursor-type frame parameter, but if it is t, that
means to use the cursor specified for the frame.
This variable specifies how to blink the cursor. Each element has the form
(on-state.off-state). Whenever the cursor type equals on-state (comparing usingequal), the corresponding off-state specifies what the cursor looks like when it blinks “off.” Both on-state and off-state should be suitable values for thecursor-typeframe parameter.There are various defaults for how to blink each type of cursor, if the type is not mentioned as an on-state here. Changes in this variable do not take effect immediately, only when you specify the
cursor-typeframe parameter.
This variable controls how the cursor looks in a window that is not selected. It supports the same values as the
cursor-typeframe parameter; also,nilmeans don't display a cursor in nonselected windows, andt(the default) means use a standard modification of the usual cursor type (solid box becomes hollow box, and bar becomes a narrower bar).
These frame parameters control the use of fonts and colors.
font-backendx (the X core font
driver) and xft (the Xft font driver). On other systems, there
is only one available font backend, so it does not make sense to
modify this frame parameter.
background-modedark or light, according
to whether the background color is a light one or a dark one.
tty-color-mode(tty-color-mode . 8) specifies use of the
ANSI escape sequences for 8 standard text colors. A value of -1 turns
off color support.
If the parameter's value is a symbol, it specifies a number through
the value of tty-color-mode-alist, and the associated number is
used instead.
screen-gammaUsual PC monitors have a screen gamma of 2.2, so color values in
Emacs, and in X windows generally, are calibrated to display properly
on a monitor with that gamma value. If you specify 2.2 for
screen-gamma, that means no correction is needed. Other values
request correction, designed to make the corrected colors appear on
your screen the way they would have appeared without correction on an
ordinary monitor with a gamma value of 2.2.
If your monitor displays colors too light, you should specify a
screen-gamma value smaller than 2.2. This requests correction
that makes colors darker. A screen gamma value of 1.5 may give good
results for LCD color displays.
alphanil value, which tells
Emacs not to set the frame opacity (leaving it to the window manager).
To prevent the frame from disappearing completely from view, the
variable frame-alpha-lower-limit defines a lower opacity limit.
If the value of the frame parameter is less than the value of this
variable, Emacs uses the latter. By default,
frame-alpha-lower-limit is 20.
The alpha frame parameter can also be a cons cell
(‘active’ . ‘inactive’), where ‘active’ is the
opacity of the frame when it is selected, and ‘inactive’ is the
opactity when it is not selected.
The following frame parameters are semi-obsolete in that they are automatically equivalent to particular face attributes of particular faces (see Standard Faces):
fontfont
attribute of the default face.
foreground-color:foreground attribute of the default face.
background-color:background attribute of the default face.
mouse-color:background
attribute of the mouse face.
cursor-color:background attribute of the cursor face.
border-color:background attribute of the border face.
scroll-bar-foregroundnil, the color for the foreground of scroll bars. It is
equivalent to the :foreground attribute of the
scroll-bar face.
scroll-bar-backgroundnil, the color for the background of scroll bars. It is
equivalent to the :background attribute of the
scroll-bar face.
You can read or change the size and position of a frame using the
frame parameters left, top, height, and
width. Whatever geometry parameters you don't specify are chosen
by the window manager in its usual fashion.
Here are some special features for working with sizes and positions. (For the precise meaning of “selected frame” used by these functions, see Input Focus.)
This function sets the position of the top left corner of frame to left and top. These arguments are measured in pixels, and normally count from the top left corner of the screen.
Negative parameter values position the bottom edge of the window up from the bottom edge of the screen, or the right window edge to the left of the right edge of the screen. It would probably be better if the values were always counted from the left and top, so that negative arguments would position the frame partly off the top or left edge of the screen, but it seems inadvisable to change that now.
These functions return the height and width of frame, measured in lines and columns. If you don't supply frame, they use the selected frame.
These functions return the height and width of the main display area of frame, measured in pixels. If you don't supply frame, they use the selected frame. For a text-only terminal, the results are in characters rather than pixels.
These values include the internal borders, and windows' scroll bars and fringes (which belong to individual windows, not to the frame itself). The exact value of the heights depends on the window-system and toolkit in use. With Gtk+, the height does not include any tool bar or menu bar. With the Motif or Lucid toolkits, it includes the tool bar but not the menu bar. In a graphical version with no toolkit, it includes both the tool bar and menu bar. For a text-only terminal, the result includes the menu bar.
These functions return the height and width of a character in frame, measured in pixels. The values depend on the choice of font. If you don't supply frame, these functions use the selected frame.
This function sets the size of frame, measured in characters; cols and rows specify the new width and height.
To set the size based on values measured in pixels, use
frame-char-heightandframe-char-widthto convert them to units of characters.
This function resizes frame to a height of lines lines. The sizes of existing windows in frame are altered proportionally to fit.
If pretend is non-
nil, then Emacs displays lines lines of output in frame, but does not change its value for the actual height of the frame. This is only useful for a terminal frame. Using a smaller height than the terminal actually implements may be useful to reproduce behavior observed on a smaller screen, or if the terminal malfunctions when using its whole screen. Setting the frame height “for real” does not always work, because knowing the correct actual size may be necessary for correct cursor positioning on a terminal frame.
This function sets the width of frame, measured in characters. The argument pretend has the same meaning as in
set-frame-height.
The older functions set-screen-height and
set-screen-width were used to specify the height and width of the
screen, in Emacs versions that did not support multiple frames. They
are semi-obsolete, but still work; they apply to the selected frame.
Here's how to examine the data in an X-style window geometry specification:
The function
x-parse-geometryconverts a standard X window geometry string to an alist that you can use as part of the argument tomake-frame.The alist describes which parameters were specified in geom, and gives the values specified for them. Each element looks like
(parameter.value). The possible parameter values areleft,top,width, andheight.For the size parameters, the value must be an integer. The position parameter names
leftandtopare not totally accurate, because some values indicate the position of the right or bottom edges instead. The value possibilities for the position parameters are: an integer, a list(+pos), or a list(-pos); as previously described (see Position Parameters).Here is an example:
(x-parse-geometry "35x70+0-0") ⇒ ((height . 70) (width . 35) (top - 0) (left . 0))
Each terminal has a list of associated parameters. These terminal parameters are mostly a convenient way of storage for terminal-local variables, but some terminal parameters have a special meaning.
This section describes functions to read and change the parameter values
of a terminal. They all accept as their argument either a terminal or
a frame; the latter means use that frame's terminal. An argument of
nil means the selected frame's terminal.
This function returns an alist listing all the parameters of terminal and their values.
This function returns the value of the parameter parameter (a symbol) of terminal. If terminal has no setting for parameter, this function returns
nil.
This function sets the parameter parm of terminal to the specified value, and returns the previous value of that parameter.
Here's a list of a few terminal parameters that have a special meaning:
background-modelight or dark.
normal-erase-is-backspacenormal-erase-is-backspace-mode is turned on or off on this
terminal. See DEL Does Not Delete.
terminal-initted
Every frame has a name parameter; this serves as the default
for the frame title which window systems typically display at the top of
the frame. You can specify a name explicitly by setting the name
frame property.
Normally you don't specify the name explicitly, and Emacs computes the
frame name automatically based on a template stored in the variable
frame-title-format. Emacs recomputes the name each time the
frame is redisplayed.
This variable specifies how to compute a name for a frame when you have not explicitly specified one. The variable's value is actually a mode line construct, just like
mode-line-format, except that the ‘%c’ and ‘%l’ constructs are ignored. See Mode Line Data.
This variable specifies how to compute the name for an iconified frame, when you have not explicitly specified the frame title. This title appears in the icon itself.
This variable is set automatically by Emacs. Its value is
twhen there are two or more frames (not counting minibuffer-only frames or invisible frames). The default value offrame-title-formatusesmultiple-framesso as to put the buffer name in the frame title only when there is more than one frame.The value of this variable is not guaranteed to be accurate except while processing
frame-title-formatoricon-title-format.
Frames remain potentially visible until you explicitly delete them. A deleted frame cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it.
This function deletes the frame frame. Unless frame is a tooltip, it first runs the hook
delete-frame-functions(each function gets one argument, frame). By default, frame is the selected frame.A frame cannot be deleted if its minibuffer is used by other frames. Normally, you cannot delete a frame if all other frames are invisible, but if force is non-
nil, then you are allowed to do so.
The function
frame-live-preturns non-nilif the frame frame has not been deleted. The possible non-nilreturn values are like those offramep. See Frames.
Some window managers provide a command to delete a window. These work
by sending a special message to the program that operates the window.
When Emacs gets one of these commands, it generates a
delete-frame event, whose normal definition is a command that
calls the function delete-frame. See Misc Events.
The function
frame-listreturns a list of all the live frames, i.e. those that have not been deleted. It is analogous tobuffer-listfor buffers, and includes frames on all terminals. The list that you get is newly created, so modifying the list doesn't have any effect on the internals of Emacs.
This function returns a list of just the currently visible frames. See Visibility of Frames. (Terminal frames always count as “visible,” even though only the selected one is actually displayed.)
The function
next-framelets you cycle conveniently through all the frames on the current display from an arbitrary starting point. It returns the “next” frame after frame in the cycle. If frame is omitted ornil, it defaults to the selected frame (see Input Focus).The second argument, minibuf, says which frames to consider:
nil- Exclude minibuffer-only frames.
visible- Consider all visible frames.
- 0
- Consider all visible or iconified frames.
- a window
- Consider only the frames using that particular window as their minibuffer.
- anything else
- Consider all frames.
Like
next-frame, but cycles through all frames in the opposite direction.
See also next-window and previous-window, in Cyclic Window Ordering.
Each window is part of one and only one frame; you can get that frame
with window-frame.
All the non-minibuffer windows in a frame are arranged in a cyclic order. The order runs from the frame's top window, which is at the upper left corner, down and to the right, until it reaches the window at the lower right corner (always the minibuffer window, if the frame has one), and then it moves back to the top. See Cyclic Window Ordering.
This returns the topmost, leftmost window of frame frame. If omitted or
nil, frame defaults to the selected frame.
At any time, exactly one window on any frame is selected within the
frame. The significance of this designation is that selecting the
frame also selects this window. Conversely, selecting a window for
Emacs with select-window also makes that window selected within
its frame. See Selecting Windows.
This function returns the window on frame that is selected within frame. If omitted or
nil, frame defaults to the selected frame.
This sets the selected window of frame frame to window. If frame is
nil, it operates on the selected frame. If frame is the selected frame, this makes window the selected window. This function returns window.Optional argument norecord non-
nilmeans to neither change the order of recently selected windows nor the buffer list (see The Buffer List).
Another function that (usually) returns one of the windows in a given
frame is minibuffer-window. See Definition of minibuffer-window.
Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected. If the frame has a minibuffer,
you can get it with minibuffer-window (see Definition of minibuffer-window).
However, you can also create a frame with no minibuffer. Such a frame
must use the minibuffer window of some other frame. When you create the
frame, you can specify explicitly the minibuffer window to use (in some
other frame). If you don't, then the minibuffer is found in the frame
which is the value of the variable default-minibuffer-frame. Its
value should be a frame that does have a minibuffer.
If you use a minibuffer-only frame, you might want that frame to raise
when you enter the minibuffer. If so, set the variable
minibuffer-auto-raise to t. See Raising and Lowering.
This variable specifies the frame to use for the minibuffer window, by default. It does not affect existing frames. It is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.
When Emacs displays its frames on several terminals (see Multiple Terminals), each terminal has its own selected frame. But only one of these is “the selected frame”: it's the frame that belongs to the terminal from which the most recent input came. That is, when Emacs runs a command that came from a certain terminal, the selected frame is the one of that terminal. Since Emacs runs only a single command at any given time, it needs to consider only one selected frame at a time; this frame is what we call the selected frame in this manual. The display on which the selected frame is shown is the selected frame's display.
Some window systems and window managers direct keyboard input to the
window object that the mouse is in; others require explicit clicks or
commands to shift the focus to various window objects. Either
way, Emacs automatically keeps track of which frame has the focus. To
explicitly switch to a different frame from a Lisp function, call
select-frame-set-input-focus.
Lisp programs can also switch frames “temporarily” by calling the
function select-frame. This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.
When using a text-only terminal, only one frame can be displayed at a
time on the terminal, so after a call to select-frame, the next
redisplay actually displays the newly selected frame. This frame
remains selected until a subsequent call to select-frame. Each
terminal frame has a number which appears in the mode line before the
buffer name (see Mode Line Variables).
This function selects frame, raises it (should it happen to be obscured by other frames) and tries to give it the X server's focus. On a text-only terminal, the next redisplay displays the new frame on the entire terminal screen. The return value of this function is not significant.
This function selects frame frame, temporarily disregarding the focus of the X server if any. The selection of frame lasts until the next time the user does something to select a different frame, or until the next time this function is called. (If you are using a window system, the previously selected frame may be restored as the selected frame after return to the command loop, because it still may have the window system's input focus.)
The specified frame becomes the selected frame, as explained above, and the terminal that frame is on becomes the selected terminal. The window selected within frame becomes the selected window. This function returns frame, or
nilif frame has been deleted.Optional argument norecord non-
nilmeans to neither change the order of recently selected windows nor the buffer list. See The Buffer List.In general, you should never use
select-framein a way that could switch to a different terminal without switching back when you're done.
Emacs cooperates with the window system by arranging to select frames as
the server and window manager request. It does so by generating a
special kind of input event, called a focus event, when
appropriate. The command loop handles a focus event by calling
handle-switch-frame. See Focus Events.
This function handles a focus event by selecting frame frame.
Focus events normally do their job by invoking this command. Don't call it for any other reason.
This function redirects focus from frame to focus-frame. This means that focus-frame will receive subsequent keystrokes and events intended for frame. After such an event, the value of
last-event-framewill be focus-frame. Also, switch-frame events specifying frame will instead select focus-frame.If focus-frame is omitted or
nil, that cancels any existing redirection for frame, which therefore once again receives its own events.One use of focus redirection is for frames that don't have minibuffers. These frames use minibuffers on other frames. Activating a minibuffer on another frame redirects focus to that frame. This puts the focus on the minibuffer's frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.
Selecting a frame can also change focus redirections. Selecting frame
bar, whenfoohad been selected, changes any redirections pointing tofooso that they point tobarinstead. This allows focus redirection to work properly when the user switches from one frame to another usingselect-window.This means that a frame whose focus is redirected to itself is treated differently from a frame whose focus is not redirected.
select-frameaffects the former but not the latter.The redirection lasts until
redirect-frame-focusis called to change it.
This option is how you inform Emacs whether the window manager transfers focus when the user moves the mouse. Non-
nilsays that it does. When this is so, the commandother-framemoves the mouse to a position consistent with the new selected frame.
A window frame may be visible, invisible, or iconified. If it is visible, you can see its contents, unless other windows cover it. If it is iconified, the frame's contents do not appear on the screen, but an icon does. (Note: because of the way in which some window managers implement the concept of multiple workspaces, or desktops, all frames on other workspaces may appear to Emacs to be iconified.) If the frame is invisible, it doesn't show on the screen, not even as an icon.
Visibility is meaningless for terminal frames, since only the selected one is actually displayed in any case.
This function makes frame frame visible. If you omit frame, it makes the selected frame visible. This does not raise the frame, but you can do that with
raise-frameif you wish (see Raising and Lowering).
This function makes frame frame invisible. If you omit frame, it makes the selected frame invisible.
Unless force is non-
nil, this function refuses to make frame invisible if all other frames are invisible..
This function iconifies frame frame. If you omit frame, it iconifies the selected frame.
This returns the visibility status of frame frame. The value is
tif frame is visible,nilif it is invisible, andiconif it is iconified.On a text-only terminal, all frames are considered visible, whether they are currently being displayed or not, and this function returns
tfor all frames.
The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See Management Parameters.
The user can iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See Misc Events.
Most window systems use a desktop metaphor. Part of this metaphor is the idea that windows are stacked in a notional third dimension perpendicular to the screen surface, and thus ordered from “highest” to “lowest.” Where two windows overlap, the one higher up covers the one underneath. Even a window at the bottom of the stack can be seen if no other window overlaps it.
A window's place in this ordering is not fixed; in fact, users tend to change the order frequently. Raising a window means moving it “up,” to the top of the stack. Lowering a window means moving it to the bottom of the stack. This motion is in the notional third dimension only, and does not change the position of the window on the screen.
With Emacs, frames constitute the windows in the metaphor sketched above. You can raise and lower frames using these functions:
This function raises frame frame (default, the selected frame). If frame is invisible or iconified, this makes it visible.
This function lowers frame frame (default, the selected frame).
If this is non-
nil, activation of the minibuffer raises the frame that the minibuffer window is in.
You can also enable auto-raise (raising automatically when a frame is selected) or auto-lower (lowering automatically when it is deselected) for any frame using frame parameters. See Management Parameters.
A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one. (See Window Configurations.)
This function returns a frame configuration list that describes the current arrangement of frames and their contents.
This function restores the state of frames described in configuration. However, this function does not restore deleted frames.
Ordinarily, this function deletes all existing frames not listed in configuration. But if nodelete is non-
nil, the unwanted frames are iconified instead.
Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves.
The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don't want to track the mouse forever—only until some other event, such as the release of a button.
This special form executes body, with generation of mouse motion events enabled. Typically, body would use
read-eventto read the motion events and modify the display accordingly. See Motion Events, for the format of mouse motion events.The value of
track-mouseis that of the last form in body. You should design body to return when it sees the up-event that indicates the release of the button, or whatever kind of event means it is time to stop tracking.
The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.
In many cases, you can avoid the need to track the mouse by using
the mouse-face text property (see Special Properties).
That works at a much lower level and runs more smoothly than
Lisp-level mouse tracking.
The functions mouse-position and set-mouse-position
give access to the current position of the mouse.
This function returns a description of the position of the mouse. The value looks like
(frame x.y), where x and y are integers giving the position in characters relative to the top left corner of the inside of frame.
If non-
nil, the value of this variable is a function formouse-positionto call.mouse-positioncalls this function just before returning, with its normal return value as the sole argument, and it returns whatever this function returns to it.This abnormal hook exists for the benefit of packages like xt-mouse.el that need to do mouse handling at the Lisp level.
This function warps the mouse to position x, y in frame frame. The arguments x and y are integers, giving the position in characters relative to the top left corner of the inside of frame. If frame is not visible, this function does nothing. The return value is not significant.
This function is like
mouse-positionexcept that it returns coordinates in units of pixels rather than units of characters.
This function warps the mouse like
set-mouse-positionexcept that x and y are in units of pixels rather than units of characters. These coordinates are not required to be within the frame.If frame is not visible, this function does nothing. The return value is not significant.
When using a window system, a Lisp program can pop up a menu so that the user can choose an alternative with the mouse.
This function displays a pop-up menu and returns an indication of what selection the user makes.
The argument position specifies where on the screen to put the top left corner of the menu. It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:
((xoffset yoffset) window)where xoffset and yoffset are coordinates, measured in pixels, counting from the top left corner of window. window may be a window or a frame.
If position is
t, it means to use the current mouse position. If position isnil, it means to precompute the key binding equivalents for the keymaps specified in menu, without actually displaying or popping up the menu.The argument menu says what to display in the menu. It can be a keymap or a list of keymaps (see Menu Keymaps). In this case, the return value is the list of events corresponding to the user's choice. This list has more than one element if the choice occurred in a submenu. (Note that
x-popup-menudoes not actually execute the command bound to that sequence of events.) On toolkits that support menu titles, the title is taken from the prompt string of menu if menu is a keymap, or from the prompt string of the first keymap in menu if it is a list of keymaps (see Defining Menus).Alternatively, menu can have the following form:
(title pane1 pane2...)where each pane is a list of form
(title item1 item2...)Each item should normally be a cons cell
(line.value), where line is a string, and value is the value to return if that line is chosen. An item can also be a string; this makes a non-selectable line in the menu.If the user gets rid of the menu without making a valid choice, for instance by clicking the mouse away from a valid choice or by typing keyboard input, then this normally results in a quit and
x-popup-menudoes not return. But if position is a mouse button event (indicating that the user invoked the menu with the mouse) then no quit occurs andx-popup-menureturnsnil.
Usage note: Don't use x-popup-menu to display a menu
if you could do the job with a prefix key defined with a menu keymap.
If you use a menu keymap to implement a menu, C-h c and C-h
a can see the individual items in that menu and provide help for them.
If instead you implement the menu by defining a command that calls
x-popup-menu, the help facilities cannot know what happens inside
that command, so they cannot give any help for the menu's items.
The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls x-popup-menu. Therefore, if you try to implement a
submenu using x-popup-menu, it cannot work with the menu bar in
an integrated fashion. This is why all menu bar submenus are
implemented with menu keymaps within the parent menu, and never with
x-popup-menu. See Menu Bar.
If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it. To make the contents vary, add
a hook function to menu-bar-update-hook to update the contents of
the menu keymap as necessary.
A dialog box is a variant of a pop-up menu—it looks a little
different, it always appears in the center of a frame, and it has just
one level and one or more buttons. The main use of dialog boxes is
for asking questions that the user can answer with “yes,” “no,”
and a few other alternatives. With a single button, they can also
force the user to acknowledge important information. The functions
y-or-n-p and yes-or-no-p use dialog boxes instead of the
keyboard, when called from commands invoked by mouse clicks.
This function displays a pop-up dialog box and returns an indication of what selection the user makes. The argument contents specifies the alternatives to offer; it has this format:
(title (string . value)...)which looks like the list that specifies a single pane for
x-popup-menu.The return value is value from the chosen alternative.
As for
x-popup-menu, an element of the list may be just a string instead of a cons cell(string.value). That makes a box that cannot be selected.If
nilappears in the list, it separates the left-hand items from the right-hand items; items that precede thenilappear on the left, and items that follow thenilappear on the right. If you don't include anilin the list, then approximately half the items appear on each side.Dialog boxes always appear in the center of a frame; the argument position specifies which frame. The possible values are as in
x-popup-menu, but the precise coordinates or the individual window don't matter; only the frame matters.If header is non-
nil, the frame title for the box is ‘Information’, otherwise it is ‘Question’. The former is used formessage-box(see message-box).In some configurations, Emacs cannot display a real dialog box; so instead it displays the same items in a pop-up menu in the center of the frame.
If the user gets rid of the dialog box without making a valid choice, for instance using the window manager, then this produces a quit and
x-popup-dialogdoes not return.
You can specify the mouse pointer style for particular text or
images using the pointer text property, and for images with the
:pointer and :map image properties. The values you can
use in these properties are text (or nil), arrow,
hand, vdrag, hdrag, modeline, and
hourglass. text stands for the usual mouse pointer
style used over text.
Over void parts of the window (parts that do not correspond to any
of the buffer contents), the mouse pointer usually uses the
arrow style, but you can specify a different style (one of
those above) by setting void-text-area-pointer.
This variable specifies the mouse pointer style for void text areas. These include the areas after the end of a line or below the last line in the buffer. The default is to use the
arrow(non-text) pointer style.
When using X, you can specify what the text pointer style
really looks like by setting the variable x-pointer-shape.
This variable specifies the pointer shape to use ordinarily in the Emacs frame, for the
textpointer style.
This variable specifies the pointer shape to use when the mouse is over mouse-sensitive text.
These variables affect newly created frames. They do not normally affect existing frames; however, if you set the mouse color of a frame, that also installs the current value of those two variables. See Font and Color Parameters.
The values you can use, to specify either of these pointer shapes, are defined in the file lisp/term/x-win.el. Use M-x apropos <RET> x-pointer <RET> to see a list of them.
The X server records a set of selections which permit transfer of data between application programs. The various selections are distinguished by selection types, represented in Emacs by symbols. X clients including Emacs can read or set the selection for any given type.
This function sets a “selection” in the X server. It takes two arguments: a selection type type, and the value to assign to it, data. If data is
nil, it means to clear out the selection. Otherwise, data may be a string, a symbol, an integer (or a cons of two integers or list of two integers), an overlay, or a cons of two markers pointing to the same buffer. An overlay or a pair of markers stands for text in the overlay or between the markers.The argument data may also be a vector of valid non-vector selection values.
Each possible type has its own selection value, which changes independently. The usual values of type are
PRIMARY,SECONDARYandCLIPBOARD; these are symbols with upper-case names, in accord with X Window System conventions. If type isnil, that stands forPRIMARY.This function returns data.
This function accesses selections set up by Emacs or by other X clients. It takes two optional arguments, type and data-type. The default for type, the selection type, is
PRIMARY.The data-type argument specifies the form of data conversion to use, to convert the raw data obtained from another X client into Lisp data. Meaningful values include
TEXT,STRING,UTF8_STRING,TARGETS,LENGTH,DELETE,FILE_NAME,CHARACTER_POSITION,NAME,LINE_NUMBER,COLUMN_NUMBER,OWNER_OS,HOST_NAME,USER,CLASS,ATOM, andINTEGER. (These are symbols with upper-case names in accord with X conventions.) The default for data-type isSTRING.
The X server also has a set of eight numbered cut buffers which can store text or other data being moved between applications. Cut buffers are considered obsolete, but Emacs supports them for the sake of X clients that still use them. Cut buffers are numbered from 0 to 7.
This function returns the contents of cut buffer number n. If omitted n defaults to 0.
This function stores string into the first cut buffer (cut buffer 0). If push is
nil, only the first cut buffer is changed. If push is non-nil, that says to move the values down through the series of cut buffers, much like the way successive kills in Emacs move down the kill ring. In other words, the previous value of the first cut buffer moves into the second cut buffer, and the second to the third, and so on through all eight cut buffers.
This variable specifies the coding system to use when reading and writing selections or the clipboard. See Coding Systems. The default is
compound-text-with-extensions, which converts to the text representation that X11 normally uses.
When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard. x-get-selection
and x-set-selection on MS-Windows support the text data type
only; if the clipboard holds other types of data, Emacs treats the
clipboard as empty.
If this is non-
nil, the Emacs yank functions consult the clipboard before the primary selection, and the kill functions store in the clipboard as well as the primary selection. Otherwise they do not access the clipboard at all. The default isnilon most systems, button MS-Windows.
When a user drags something from another application over Emacs, that other
application expects Emacs to tell it if Emacs can handle the data that is
dragged. The variable x-dnd-test-function is used by Emacs to determine
what to reply. The default value is x-dnd-default-test-function
which accepts drops if the type of the data to be dropped is present in
x-dnd-known-types. You can customize x-dnd-test-function and/or
x-dnd-known-types if you want Emacs to accept or reject drops based
on some other criteria.
If you want to change the way Emacs handles drop of different types
or add a new type, customize x-dnd-types-alist. This requires
detailed knowledge of what types other applications use for drag and
drop.
When an URL is dropped on Emacs it may be a file, but it may also be
another URL type (ftp, http, etc.). Emacs first checks
dnd-protocol-alist to determine what to do with the URL. If
there is no match there and if browse-url-browser-function is
an alist, Emacs looks for a match there. If no match is found the
text for the URL is inserted. If you want to alter Emacs behavior,
you can customize these variables.
A color name is text (usually in a string) that specifies a color. Symbolic names such as ‘black’, ‘white’, ‘red’, etc., are allowed; use M-x list-colors-display to see a list of defined names. You can also specify colors numerically in forms such as ‘#rgb’ and ‘RGB:r/g/b’, where r specifies the red level, g specifies the green level, and b specifies the blue level. You can use either one, two, three, or four hex digits for r; then you must use the same number of hex digits for all g and b as well, making either 3, 6, 9 or 12 hex digits in all. (See the documentation of the X Window System for more details about numerical RGB specification of colors.)
These functions provide a way to determine which color names are valid, and what they look like. In some cases, the value depends on the selected frame, as described below; see Input Focus, for the meaning of the term “selected frame.”
To read user input of color names with completion, use
read-color (see read-color).
This function reports whether a color name is meaningful. It returns
tif so; otherwise,nil. The argument frame says which frame's display to ask about; if frame is omitted ornil, the selected frame is used.Note that this does not tell you whether the display you are using really supports that color. When using X, you can ask for any defined color on any kind of display, and you will get some result—typically, the closest it can do. To determine whether a frame can really display a certain color, use
color-supported-p(see below).This function used to be called
x-color-defined-p, and that name is still supported as an alias.
This function returns a list of the color names that are defined and supported on frame frame (default, the selected frame). If frame does not support colors, the value is
nil.This function used to be called
x-defined-colors, and that name is still supported as an alias.
This returns
tif frame can really display the color color (or at least something close to it). If frame is omitted ornil, the question applies to the selected frame.Some terminals support a different set of colors for foreground and background. If background-p is non-
nil, that means you are asking whether color can be used as a background; otherwise you are asking whether it can be used as a foreground.The argument color must be a valid color name.
This returns
tif color is a shade of gray, as defined on frame's display. If frame is omitted ornil, the question applies to the selected frame. If color is not a valid color name, this function returnsnil.
This function returns a value that describes what color should ideally look like on frame. If color is defined, the value is a list of three integers, which give the amount of red, the amount of green, and the amount of blue. Each integer ranges in principle from 0 to 65535, but some displays may not use the full range. This three-element list is called the rgb values of the color.
If color is not defined, the value is
nil.(color-values "black") ⇒ (0 0 0) (color-values "white") ⇒ (65280 65280 65280) (color-values "red") ⇒ (65280 0 0) (color-values "pink") ⇒ (65280 49152 51968) (color-values "hungry") ⇒ nilThe color values are returned for frame's display. If frame is omitted or
nil, the information is returned for the selected frame's display. If the frame cannot display colors, the value isnil.This function used to be called
x-color-values, and that name is still supported as an alias.
Text-only terminals usually support only a small number of colors, and the computer uses small integers to select colors on the terminal. This means that the computer cannot reliably tell what the selected color looks like; instead, you have to inform your application which small integers correspond to which colors. However, Emacs does know the standard set of colors and will try to use them automatically.
The functions described in this section control how terminal colors are used by Emacs.
Several of these functions use or return rgb values, described in Color Names.
These functions accept a display (either a frame or the name of a terminal) as an optional argument. We hope in the future to make Emacs support different colors on different text-only terminals; then this argument will specify which terminal to operate on (the default being the selected frame's terminal; see Input Focus). At present, though, the frame argument has no effect.
This function associates the color name name with color number number on the terminal.
The optional argument rgb, if specified, is an rgb value, a list of three numbers that specify what the color actually looks like. If you do not specify rgb, then this color cannot be used by
tty-color-approximateto approximate other colors, because Emacs will not know what it looks like.
This function clears the table of defined colors for a text-only terminal.
This function returns an alist recording the known colors supported by a text-only terminal.
Each element has the form
(name number.rgb)or(name number). Here, name is the color name, number is the number used to specify it to the terminal. If present, rgb is a list of three color values (for red, green, and blue) that says what the color actually looks like.
This function finds the closest color, among the known colors supported for display, to that described by the rgb value rgb (a list of color values). The return value is an element of
tty-color-alist.
This function finds the closest color to color among the known colors supported for display and returns its index (an integer). If the name color is not defined, the value is
nil.
This section describes some of the functions and variables for querying and using X resources, or their equivalent on your operating system. See X Resources, for more information about X resources.
The function
x-get-resourceretrieves a resource value from the X Window defaults database.Resources are indexed by a combination of a key and a class. This function searches using a key of the form ‘instance.attribute’ (where instance is the name under which Emacs was invoked), and using ‘Emacs.class’ as the class.
The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is ‘instance.component.attribute’, and the class is ‘Emacs.class.subclass’.
This variable specifies the application name that
x-get-resourceshould look up. The default value is"Emacs". You can examine X resources for application names other than “Emacs” by binding this variable to some other string, around a call tox-get-resource.
This variable specifies the instance name that
x-get-resourceshould look up. The default value is the name Emacs was invoked with, or the value specified with the ‘-name’ or ‘-rn’ switches.
To illustrate some of the above, suppose that you have the line:
xterm.vt100.background: yellow
in your X resources file (whose name is usually ~/.Xdefaults or ~/.Xresources). Then:
(let ((x-resource-class "XTerm") (x-resource-name "xterm"))
(x-get-resource "vt100.background" "VT100.Background"))
⇒ "yellow"
(let ((x-resource-class "XTerm") (x-resource-name "xterm"))
(x-get-resource "background" "VT100" "vt100" "Background"))
⇒ "yellow"
If this variable is non-
nil, Emacs does not look up X resources, and X resources do not have any effect when creating new frames.
The functions in this section describe the basic capabilities of a particular display. Lisp programs can use them to adapt their behavior to what the display can do. For example, a program that ordinarily uses a popup menu could use the minibuffer if popup menus are not supported.
The optional argument display in these functions specifies which
display to ask the question about. It can be a display name, a frame
(which designates the display that frame is on), or nil (which
refers to the selected frame's display, see Input Focus).
See Color Names, Text Terminal Colors, for other functions to obtain information about displays.
This function returns
tif popup menus are supported on display,nilif not. Support for popup menus requires that the mouse be available, since the user cannot choose menu items without a mouse.
This function returns
tif display is a graphic display capable of displaying several frames and several different fonts at once. This is true for displays that use a window system such as X, and false for text-only terminals.
This function returns
tif display has a mouse available,nilif not.
This function returns
tif the screen is a color screen. It used to be calledx-display-color-p, and that name is still supported as an alias.
This function returns
tif the screen can display shades of gray. (All color displays can do this.)
This function returns non-
nilif all the face attributes in attributes are supported (see Face Attributes).The definition of `supported' is somewhat heuristic, but basically means that a face containing all the attributes in attributes, when merged with the default face for display, can be represented in a way that's
- different in appearance than the default face, and
- `close in spirit' to what the attributes specify, if not exact.
Point (2) implies that a
:weight blackattribute will be satisfied by any display that can display bold, as will:foreground "yellow"as long as some yellowish color can be displayed, but:slant italicwill not be satisfied by the tty display code's automatic substitution of a `dim' face for italic.
This function returns
tif display supports selections. Windowed displays normally support selections, but they may also be supported in some other cases.
This function returns
tif display can display images. Windowed displays ought in principle to handle images, but some systems lack the support for that. On a display that does not support images, Emacs cannot display a tool bar.
This function returns the number of screens associated with the display.
This function returns the height of the screen in pixels. On a character terminal, it gives the height in characters.
For graphical terminals, note that on “multi-monitor” setups this refers to the pixel width for all physical monitors associated with display. See Multiple Terminals.
This function returns the width of the screen in pixels. On a character terminal, it gives the width in characters.
For graphical terminals, note that on “multi-monitor” setups this refers to the pixel width for all physical monitors associated with display. See Multiple Terminals.
This function returns the height of the screen in millimeters, or
nilif Emacs cannot get that information.
This function returns the width of the screen in millimeters, or
nilif Emacs cannot get that information.
This variable allows the user to specify the dimensions of graphical displays returned by
display-mm-heightanddisplay-mm-widthin case the system provides incorrect values.
This function returns the backing store capability of the display. Backing store means recording the pixels of windows (and parts of windows) that are not exposed, so that when exposed they can be displayed very quickly.
Values can be the symbols
always,when-mapped, ornot-useful. The function can also returnnilwhen the question is inapplicable to a certain kind of display.
This function returns non-
nilif the display supports the SaveUnder feature. That feature is used by pop-up windows to save the pixels they obscure, so that they can pop down quickly.
This function returns the number of planes the display supports. This is typically the number of bits per pixel. For a tty display, it is log to base two of the number of colors supported.
This function returns the visual class for the screen. The value is one of the symbols
static-gray,gray-scale,static-color,pseudo-color,true-color, anddirect-color.
This function returns the number of color cells the screen supports.
These functions obtain additional information specifically about X displays.
This function returns the list of version numbers of the X server running the display. The value is a list of three integers: the major and minor version numbers of the X protocol, and the distributor-specific release number of the X server software itself.
This function returns the “vendor” that provided the X server software (as a string). Really this means whoever distributes the X server.
When the developers of X labelled software distributors as “vendors,” they showed their false assumption that no system could ever be developed and distributed noncommercially.
A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character “at” a position, meaning the character after that position.
Positions are usually represented as integers starting from 1, but can also be represented as markers—special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. Functions that expect an argument to be a position (an integer), but accept a marker as a substitute, normally ignore which buffer the marker points into; they convert the marker to an integer, and use that integer, exactly as if you had passed the integer as the argument, even if the marker points to the “wrong” buffer. A marker that points nowhere cannot convert to an integer; using it instead of an integer causes an error. See Markers.
See also the “field” feature (see Fields), which provides functions that are used by many cursor-motion commands.
Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits.
The value of point is a number no less than 1, and no greater than the buffer size plus 1. If narrowing is in effect (see Narrowing), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See Window Point, for more details.
This function returns the value of point in the current buffer, as an integer.
(point) ⇒ 175
This function returns the minimum accessible value of point in the current buffer. This is normally 1, but if narrowing is in effect, it is the position of the start of the region that you narrowed to. (See Narrowing.)
This function returns the maximum accessible value of point in the current buffer. This is
(1+ (buffer-size)), unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (See Narrowing.)
This function returns
(point-max)if flag is greater than 0,(point-min)otherwise. The argument flag must be a number.
This function returns the total number of characters in the current buffer. In the absence of any narrowing (see Narrowing),
point-maxreturns a value one larger than this.If you specify a buffer, buffer, then the value is the size of buffer.
(buffer-size) ⇒ 35 (point-max) ⇒ 36
Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See Point.
These functions move point based on a count of characters.
goto-char is the fundamental primitive; the other functions use
that.
This function sets point in the current buffer to the value position. If position is less than 1, it moves point to the beginning of the buffer. If position is greater than the length of the buffer, it moves point to the end.
If narrowing is in effect, position still counts from the beginning of the buffer, but point cannot go outside the accessible portion. If position is out of range,
goto-charmoves point to the beginning or the end of the accessible portion.When this function is called interactively, position is the numeric prefix argument, if provided; otherwise it is read from the minibuffer.
goto-charreturns position.
This function moves point count characters forward, towards the end of the buffer (or backward, towards the beginning of the buffer, if count is negative). If count is
nil, the default is 1.If this attempts to move past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), it signals an error with error symbol
beginning-of-bufferorend-of-buffer.In an interactive call, count is the numeric prefix argument.
This is just like
forward-charexcept that it moves in the opposite direction.
These functions for parsing words use the syntax table to decide whether a given character is part of a word. See Syntax Tables.
This function moves point forward count words (or backward if count is negative). If count is
nil, it moves forward one word.“Moving one word” means moving until point crosses a word-constituent character and then encounters a word-separator character. However, this function cannot move point past the boundary of the accessible portion of the buffer, or across a field boundary (see Fields). The most common case of a field boundary is the end of the prompt in the minibuffer.
If it is possible to move count words, without being stopped prematurely by the buffer boundary or a field boundary, the value is
t. Otherwise, the return value isniland point stops at the buffer boundary or field boundary.If
inhibit-field-text-motionis non-nil, this function ignores field boundaries.In an interactive call, count is specified by the numeric prefix argument. If count is omitted or
nil, it defaults to 1.
This function is just like
forward-word, except that it moves backward until encountering the front of a word, rather than forward.
This variable affects the behavior of
forward-wordand everything that uses it. If it is non-nil, then characters in the “escape” and “character quote” syntax classes count as part of words. Otherwise, they do not.
If this variable is non-
nil, certain motion functions includingforward-word,forward-sentence, andforward-paragraphignore field boundaries.
To move point to the beginning of the buffer, write:
(goto-char (point-min))
Likewise, to move to the end of the buffer, use:
(goto-char (point-max))
Here are two commands that users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area.
This function moves point to the beginning of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position (except in Transient Mark mode, if the mark is already active, it does not set the mark.)
If n is non-
nil, then it puts point n tenths of the way from the beginning of the accessible portion of the buffer. In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults tonil.Warning: Don't use this function in Lisp programs!
This function moves point to the end of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position (except in Transient Mark mode when the mark is already active). If n is non-
nil, then it puts point n tenths of the way from the end of the accessible portion of the buffer.In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults to
nil.Warning: Don't use this function in Lisp programs!
Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed.
This function moves point to the beginning of the current line. With an argument count not
nilor 1, it moves forward count−1 lines and then to the beginning of the line.This function does not move point across a field boundary (see Fields) unless doing so would move beyond there to a different line; therefore, if count is
nilor 1, and point starts at a field boundary, point does not move. To ignore field boundaries, either bindinhibit-field-text-motiontot, or use theforward-linefunction instead. For instance,(forward-line 0)does the same thing as(beginning-of-line), except that it ignores field boundaries.If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
Return the position that
(beginning-of-linecount)would move to.
This function moves point to the end of the current line. With an argument count not
nilor 1, it moves forward count−1 lines and then to the end of the line.This function does not move point across a field boundary (see Fields) unless doing so would move beyond there to a different line; therefore, if count is
nilor 1, and point starts at a field boundary, point does not move. To ignore field boundaries, bindinhibit-field-text-motiontot.If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
Return the position that
(end-of-linecount)would move to.
This function moves point forward count lines, to the beginning of the line. If count is negative, it moves point −count lines backward, to the beginning of a line. If count is zero, it moves point to the beginning of the current line. If count is
nil, that means 1.If
forward-lineencounters the beginning or end of the buffer (or of the accessible portion) before finding that many lines, it sets point there. No error is signaled.
forward-linereturns the difference between count and the number of lines actually moved. If you attempt to move down five lines from the beginning of a buffer that has only three lines, point stops at the end of the last line, and the value will be 2.In an interactive call, count is the numeric prefix argument.
This function returns the number of lines between the positions start and end in the current buffer. If start and end are equal, then it returns 0. Otherwise it returns at least 1, even if start and end are on the same line. This is because the text between them, considered in isolation, must contain at least one line unless it is empty.
Here is an example of using
count-lines:(defun current-line () "Return the vertical position of point..." (+ (count-lines (window-start) (point)) (if (= (current-column) 0) 1 0)))
This function returns the line number in the current buffer corresponding to the buffer position pos. If pos is
nilor omitted, the current buffer position is used.
Also see the functions bolp and eolp in Near Point.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. In these cases,
vertical-motion moves point much like forward-line.
See Truncation.
Because the width of a given string depends on the flags that control
the appearance of certain characters, vertical-motion behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows). See Usual Display.
These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned. If you intend to use them heavily, Emacs provides caches which may improve the performance of your code. See cache-long-line-scans.
This function moves point to the start of the screen line count screen lines down from the screen line containing point. If count is negative, it moves up instead.
The count argument can be a cons cell,
(cols.lines), instead of an integer. Then the function moves by lines screen lines, and puts point cols columns from the start of that screen line.The return value is the number of screen lines over which point was moved. The value may be less in absolute value than count if the beginning or end of the buffer was reached.
The window window is used for obtaining parameters such as the width, the horizontal scrolling, and the display table. But
vertical-motionalways operates on the current buffer, even if window currently displays some other buffer.
This function returns the number of screen lines in the text from beg to end. The number of screen lines may be different from the number of actual lines, due to line continuation, the display table, etc. If beg and end are
nilor omitted, they default to the beginning and end of the accessible portion of the buffer.If the region ends with a newline, that is ignored unless the optional third argument count-final-newline is non-
nil.The optional fourth argument window specifies the window for obtaining parameters such as width, horizontal scrolling, and so on. The default is to use the selected window's parameters.
Like
vertical-motion,count-screen-linesalways uses the current buffer, regardless of which buffer is displayed in window. This makes possible to usecount-screen-linesin any buffer, whether or not it is currently displayed in some window.
This function moves point with respect to the text currently displayed in the selected window. It moves point to the beginning of the screen line count screen lines from the top of the window. If count is negative, that specifies a position −count lines from the bottom (or the last line of the buffer, if the buffer ends above the specified screen position).
If count is
nil, then point moves to the beginning of the line in the middle of the window. If the absolute value of count is greater than the size of the window, then point moves to the place that would appear on that screen line if the window were tall enough. This will probably cause the next redisplay to scroll to bring that location onto the screen.In an interactive call, count is the numeric prefix argument.
The value returned is the window line number point has moved to, with the top line in the window numbered 0.
This function scans the current buffer, calculating screen positions. It scans the buffer forward from position from, assuming that is at screen coordinates frompos, to position to or coordinates topos, whichever comes first. It returns the ending buffer position and screen coordinates.
The coordinate arguments frompos and topos are cons cells of the form
(hpos.vpos).The argument width is the number of columns available to display text; this affects handling of continuation lines.
nilmeans the actual number of usable text columns in the window, which is equivalent to the value returned by(window-width window).The argument offsets is either
nilor a cons cell of the form(hscroll.tab-offset). Here hscroll is the number of columns not being displayed at the left margin; most callers get this by callingwindow-hscroll. Meanwhile, tab-offset is the offset between column numbers on the screen and column numbers in the buffer. This can be nonzero in a continuation line, when the previous screen lines' widths do not add up to a multiple oftab-width. It is always zero in a non-continuation line.The window window serves only to specify which display table to use.
compute-motionalways operates on the current buffer, regardless of what buffer is displayed in window.The return value is a list of five elements:
(pos hpos vpos prevhpos contin)Here pos is the buffer position where the scan stopped, vpos is the vertical screen position, and hpos is the horizontal screen position.
The result prevhpos is the horizontal position one character back from pos. The result contin is
tif the last line was continued after (or within) the previous character.For example, to find the buffer position of column col of screen line line of a certain window, pass the window's display start location as from and the window's upper-left coordinates as frompos. Pass the buffer's
(point-max)as to, to limit the scan to the end of the accessible portion of the buffer, and pass line and col as topos. Here's a function that does this:(defun coordinates-of-position (col line) (car (compute-motion (window-start) '(0 . 0) (point-max) (cons col line) (window-width) (cons (window-hscroll) 0) (selected-window))))When you use
compute-motionfor the minibuffer, you need to useminibuffer-prompt-widthto get the horizontal position of the beginning of the first screen line. See Minibuffer Contents.
Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see Syntax Tables. See Parsing Expressions, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see Commands for Editing with Parentheses.
This function moves forward across arg (default 1) balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
This function moves backward across arg (default 1) balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
This function moves forward out of arg (default 1) levels of parentheses. A negative argument means move backward but still to a less deep spot.
This function moves forward into arg (default 1) levels of parentheses. A negative argument means move backward but still go deeper in parentheses (−arg levels).
This function moves forward across arg (default 1) balanced expressions. Balanced expressions include both those delimited by parentheses and other kinds, such as words and string constants. See Parsing Expressions. For example,
---------- Buffer: foo ---------- (concat-!- "foo " (car x) y z) ---------- Buffer: foo ---------- (forward-sexp 3) ⇒ nil ---------- Buffer: foo ---------- (concat "foo " (car x) y-!- z) ---------- Buffer: foo ----------
This function moves backward across arg (default 1) balanced expressions.
This function moves back to the argth beginning of a defun. If arg is negative, this actually moves forward, but it still moves to the beginning of a defun, not to the end of one. arg defaults to 1.
This function moves forward to the argth end of a defun. If arg is negative, this actually moves backward, but it still moves to the end of a defun, not to the beginning of one. arg defaults to 1.
If non-
nil, this buffer-local variable holds a regular expression that specifies what text can appear before the open-parenthesis that starts a defun. That is to say, a defun begins on a line that starts with a match for this regular expression, followed by a character with open-parenthesis syntax.
If this variable's value is non-
nil, an open parenthesis in column 0 is considered to be the start of a defun. If it isnil, an open parenthesis in column 0 has no special meaning. The default ist.
If non-
nil, this variable holds a function for finding the beginning of a defun. The functionbeginning-of-defuncalls this function instead of using its normal method, passing it its optional argument. If the argument is non-nil, the function should move back by that many functions, likebeginning-of-defundoes.
If non-
nil, this variable holds a function for finding the end of a defun. The functionend-of-defuncalls this function instead of using its normal method.
The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see Motion and Syntax.
These functions convert the set string to multibyte if the buffer is multibyte, and they convert it to unibyte if the buffer is unibyte, as the search functions do (see Searching and Matching).
This function moves point in the current buffer forward, skipping over a given set of characters. It examines the character following point, then advances point if the character matches character-set. This continues until it reaches a character that does not match. The function returns the number of characters moved over.
The argument character-set is a string, like the inside of a ‘[...]’ in a regular expression except that ‘]’ does not terminate it, and ‘\’ quotes ‘^’, ‘-’ or ‘\’. Thus,
"a-zA-Z"skips over all letters, stopping before the first nonletter, and"^a-zA-Z"skips nonletters stopping before the first letter. See See Regular Expressions. Character classes can also be used, e.g."[:alnum:]". See see Char Classes.If limit is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before limit.
In the following example, point is initially located directly before the ‘T’. After the form is evaluated, point is located at the end of that line (between the ‘t’ of ‘hat’ and the newline). The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (skip-chars-forward "a-zA-Z ") ⇒ 18 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function moves point backward, skipping characters that match character-set, until limit. It is just like
skip-chars-forwardexcept for the direction of motion.The return value indicates the distance traveled. It is an integer that is zero or less.
It is often useful to move point “temporarily” within a localized
portion of the program, or to switch buffers temporarily. This is
called an excursion, and it is done with the save-excursion
special form. This construct initially remembers the identity of the
current buffer, and its values of point and the mark, and restores them
after the completion of the excursion.
The forms for saving and restoring the configuration of windows are
described elsewhere (see Window Configurations, and see Frame Configurations). When only the identity of the current buffer needs
to be saved and restored, it is preferable to use
save-current-buffer instead.
The
save-excursionspecial form saves the identity of the current buffer and the values of point and the mark in it, evaluates body, and finally restores the buffer and its saved values of point and the mark. All three saved values are restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).The
save-excursionspecial form is the standard way to move point within one part of a program and avoid affecting the rest of the program. It is used more than 4000 times in the Lisp sources of Emacs.
save-excursiondoes not save the values of point and the mark for other buffers, so changes in other buffers remain in effect aftersave-excursionexits.Likewise,
save-excursiondoes not restore window-buffer correspondences altered by functions such asswitch-to-buffer. One way to restore these correspondences, and the selected window, is to usesave-window-excursioninsidesave-excursion(see Window Configurations).The value returned by
save-excursionis the result of the last form in body, ornilif no body forms were given.(save-excursion forms) == (let ((old-buf (current-buffer)) (old-pnt (point-marker)) (old-mark (copy-marker (mark-marker)))) (unwind-protect (progn forms) (set-buffer old-buf) (goto-char old-pnt) (set-marker (mark-marker) old-mark)))
Warning: Ordinary insertion of text adjacent to the saved
point value relocates the saved value, just as it relocates all markers.
More precisely, the saved value is a marker with insertion type
nil. See Marker Insertion Types. Therefore, when the saved
point value is restored, it normally comes before the inserted text.
Although save-excursion saves the location of the mark, it does
not prevent functions which modify the buffer from setting
deactivate-mark, and thus causing the deactivation of the mark
after the command finishes. See The Mark.
Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.
Narrowing is specified with two buffer positions which become the beginning and end of the accessible portion. For most editing commands and most Emacs primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion.
Values such as positions or line numbers, which usually count from the beginning of the buffer, do so despite narrowing, but the functions which use them refuse to operate on text that is inaccessible.
The commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing.
If you need to display in a single buffer several very different types of text, consider using an alternative facility described in Swapping Text.
This function sets the accessible portion of the current buffer to start at start and end at end. Both arguments should be character positions.
In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).
This function sets the accessible portion of the current buffer to include just the current page. An optional first argument move-count non-
nilmeans to move forward or backward by move-count pages and then narrow to one page. The variablepage-delimiterspecifies where pages start and end (see Standard Regexps).In an interactive call, move-count is set to the numeric prefix argument.
This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called widening. It is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
This special form saves the current bounds of the accessible portion, evaluates the body forms, and finally restores the saved bounds, thus restoring the same state of narrowing (or absence thereof) formerly in effect. The state of narrowing is restored even in the event of an abnormal exit via
throwor error (see Nonlocal Exits). Therefore, this construct is a clean way to narrow a buffer temporarily.The value returned by
save-restrictionis that returned by the last form in body, ornilif no body forms were given.Caution: it is easy to make a mistake when using the
save-restrictionconstruct. Read the entire description here before you try it.If body changes the current buffer,
save-restrictionstill restores the restrictions on the original buffer (the buffer whose restrictions it saved from), but it does not restore the identity of the current buffer.
save-restrictiondoes not restore point and the mark; usesave-excursionfor that. If you use bothsave-restrictionandsave-excursiontogether,save-excursionshould come first (on the outside). Otherwise, the old point value would be restored with temporary narrowing still in effect. If the old point value were outside the limits of the temporary narrowing, this would fail to restore it accurately.Here is a simple example of correct use of
save-restriction:---------- Buffer: foo ---------- This is the contents of foo This is the contents of foo This is the contents of foo-!- ---------- Buffer: foo ---------- (save-excursion (save-restriction (goto-char 1) (forward-line 2) (narrow-to-region 1 (point)) (goto-char (point-min)) (replace-string "foo" "bar"))) ---------- Buffer: foo ---------- This is the contents of bar This is the contents of bar This is the contents of foo-!- ---------- Buffer: foo ----------
A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it.
A marker specifies a buffer and a position in that buffer. The marker can be used to represent a position in the functions that require one, just as an integer could be used. In that case, the marker's buffer is normally ignored. Of course, a marker used in this way usually points to a position in the buffer that the function operates on, but that is entirely the programmer's responsibility. See Positions, for a complete description of positions.
A marker has three attributes: the marker position, the marker buffer, and the insertion type. The marker position is an integer that is equivalent (at a given time) to the marker as a position in that buffer. But the marker's position value can change often during the life of the marker. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker.
Deleting text around a marker's position leaves the marker between the
characters immediately before and after the deleted text. Inserting
text at the position of a marker normally leaves the marker either in
front of or after the new text, depending on the marker's insertion
type (see Marker Insertion Types)—unless the insertion is done
with insert-before-markers (see Insertion).
Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Unreferenced markers are garbage collected eventually, but until then will continue to use time if they do point somewhere.
Because it is common to perform arithmetic operations on a marker
position, most of the arithmetic operations (including + and
-) accept markers as arguments. In such cases, the marker
stands for its current position.
Here are examples of creating markers, setting markers, and moving point to markers:
;; Make a new marker that initially does not point anywhere: (setq m1 (make-marker)) ⇒ #<marker in no buffer> ;; Setm1to point between the 99th and 100th characters ;; in the current buffer: (set-marker m1 100) ⇒ #<marker at 100 in markers.texi> ;; Now insert one character at the beginning of the buffer: (goto-char (point-min)) ⇒ 1 (insert "Q") ⇒ nil ;;m1is updated appropriately. m1 ⇒ #<marker at 101 in markers.texi> ;; Two markers that point to the same position ;; are noteq, but they areequal. (setq m2 (copy-marker m1)) ⇒ #<marker at 101 in markers.texi> (eq m1 m2) ⇒ nil (equal m1 m2) ⇒ t ;; When you are finished using a marker, make it point nowhere. (set-marker m1 nil) ⇒ #<marker in no buffer>
You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers.
This function returns
tif object is a marker,nilotherwise. Note that integers are not markers, even though many functions will accept either a marker or an integer.
This function returns
tif object is an integer or a marker,nilotherwise.
This function returns
tif object is a number (either integer or floating point) or a marker,nilotherwise.
When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker.
The next four functions all return markers with insertion type
nil. See Marker Insertion Types.
This function returns a newly created marker that does not point anywhere.
(make-marker) ⇒ #<marker in no buffer>
This function returns a new marker that points to the present position of point in the current buffer. See Point. For an example, see
copy-marker, below.
This function returns a new marker that points to the beginning of the accessible portion of the buffer. This will be the beginning of the buffer unless narrowing is in effect. See Narrowing.
This function returns a new marker that points to the end of the accessible portion of the buffer. This will be the end of the buffer unless narrowing is in effect. See Narrowing.
Here are examples of this function and
point-min-marker, shown in a buffer containing a version of the source file for the text of this chapter.(point-min-marker) ⇒ #<marker at 1 in markers.texi> (point-max-marker) ⇒ #<marker at 15573 in markers.texi> (narrow-to-region 100 200) ⇒ nil (point-min-marker) ⇒ #<marker at 100 in markers.texi> (point-max-marker) ⇒ #<marker at 200 in markers.texi>
If passed a marker as its argument,
copy-markerreturns a new marker that points to the same place and the same buffer as does marker-or-integer. If passed an integer as its argument,copy-markerreturns a new marker that points to position marker-or-integer in the current buffer.The new marker's insertion type is specified by the argument insertion-type. See Marker Insertion Types.
If passed an integer argument less than 1,
copy-markerreturns a new marker that points to the beginning of the current buffer. If passed an integer argument greater than the length of the buffer,copy-markerreturns a new marker that points to the end of the buffer.(copy-marker 0) ⇒ #<marker at 1 in markers.texi> (copy-marker 20000) ⇒ #<marker at 7572 in markers.texi>An error is signaled if marker is neither a marker nor an integer.
Two distinct markers are considered equal (even though not
eq) to each other if they have the same position and buffer, or
if they both point nowhere.
(setq p (point-marker))
⇒ #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
⇒ #<marker at 2139 in markers.texi>
(eq p q)
⇒ nil
(equal p q)
⇒ t
This section describes the functions for accessing the components of a marker object.
This function returns the position that marker points to, or
nilif it points nowhere.
This function returns the buffer that marker points into, or
nilif it points nowhere.(setq m (make-marker)) ⇒ #<marker in no buffer> (marker-position m) ⇒ nil (marker-buffer m) ⇒ nil (set-marker m 3770 (current-buffer)) ⇒ #<marker at 3770 in markers.texi> (marker-buffer m) ⇒ #<buffer markers.texi> (marker-position m) ⇒ 3770
This function returns
tif one or more markers point at position position in the current buffer.
When you insert text directly at the place where a marker points,
there are two possible ways to relocate that marker: it can point before
the inserted text, or point after it. You can specify which one a given
marker should do by setting its insertion type. Note that use of
insert-before-markers ignores markers' insertion types, always
relocating a marker to point after the inserted text.
This function sets the insertion type of marker marker to type. If type is
t, marker will advance when text is inserted at its position. If type isnil, marker does not advance when text is inserted there.
This function reports the current insertion type of marker.
Most functions that create markers, without an argument allowing to
specify the insertion type, create them with insertion type
nil. Also, the mark has, by default, insertion type
nil.
This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it—otherwise, confusing things may happen in other parts of Emacs.
This function moves marker to position in buffer. If buffer is not provided, it defaults to the current buffer.
If position is less than 1,
set-markermoves marker to the beginning of the buffer. If position is greater than the size of the buffer,set-markermoves marker to the end of the buffer. If position isnilor a marker that points nowhere, then marker is set to point nowhere.The value returned is marker.
(setq m (point-marker)) ⇒ #<marker at 4714 in markers.texi> (set-marker m 55) ⇒ #<marker at 55 in markers.texi> (setq b (get-buffer "foo")) ⇒ #<buffer foo> (set-marker m 0 b) ⇒ #<marker at 1 in foo>
Each buffer has a special marker, which is designated the mark. When a buffer is newly created, this marker exists but does not point anywhere; this means that the mark “doesn't exist” in that buffer yet. Subsequent commands can set the mark.
The mark specifies a position to bound a range of text for many
commands, such as kill-region and indent-rigidly. These
commands typically act on the text between point and the mark, which
is called the region. If you are writing a command that
operates on the region, don't examine the mark directly; instead, use
interactive with the ‘r’ specification. This provides the
values of point and the mark as arguments to the command in an
interactive call, but permits other Lisp programs to specify arguments
explicitly. See Interactive Codes.
Some commands set the mark as a side-effect. Commands should do
this only if it has a potential use to the user, and never for their
own internal purposes. For example, the replace-regexp command
sets the mark to the value of point before doing any replacements,
because this enables the user to move back there conveniently after
the replace is finished.
Once the mark “exists” in a buffer, it normally never ceases to
exist. However, it may become inactive, if Transient Mark mode
is enabled. The buffer-local variable mark-active, if
non-nil, means that the mark is active. A command can call the
function deactivate-mark to deactivate the mark directly, or it
can request deactivation of the mark upon return to the editor command
loop by setting the variable deactivate-mark to a
non-nil value.
If Transient Mode is enabled, certain editing commands that normally apply to text near point, apply instead to the region when the mark is active. This is the main motivation for using Transient Mark mode. (Another is that this enables highlighting of the region when the mark is active. See Display.)
In addition to the mark, each buffer has a mark ring which is a
list of markers containing previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The variable mark-ring-max specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.
There is also a separate global mark ring, but that is used only in a few particular user-level commands, and is not relevant to Lisp programming. So we do not describe it here.
This function returns the current buffer's mark position as an integer, or
nilif no mark has ever been set in this buffer.If Transient Mark mode is enabled, and
mark-even-if-inactiveisnil,marksignals an error if the mark is inactive. However, if force is non-nil, thenmarkdisregards inactivity of the mark, and returns the mark position (ornil) anyway.
This function returns the marker that represents the current buffer's mark. It is not a copy, it is the marker used internally. Therefore, changing this marker's position will directly affect the buffer's mark. Don't do that unless that is the effect you want.
(setq m (mark-marker)) ⇒ #<marker at 3420 in markers.texi> (set-marker m 100) ⇒ #<marker at 100 in markers.texi> (mark-marker) ⇒ #<marker at 100 in markers.texi>Like any marker, this marker can be set to point at any buffer you like. If you make it point at any buffer other than the one of which it is the mark, it will yield perfectly consistent, but rather odd, results. We recommend that you not do it!
This function sets the mark to position, and activates the mark. The old value of the mark is not pushed onto the mark ring.
Please note: Use this function only if you want the user to see that the mark has moved, and you want the previous mark position to be lost. Normally, when a new mark is set, the old one should go on the
mark-ring. For this reason, most applications should usepush-markandpop-mark, notset-mark.Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user's convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:
(let ((beg (point))) (forward-line 1) (delete-region beg (point))).
This function sets the current buffer's mark to position, and pushes a copy of the previous mark onto
mark-ring. If position isnil, then the value of point is used.push-markreturnsnil.The function
push-marknormally does not activate the mark. To do that, specifytfor the argument activate.A ‘Mark set’ message is displayed unless nomsg is non-
nil.
This function pops off the top element of
mark-ringand makes that mark become the buffer's actual mark. This does not move point in the buffer, and it does nothing ifmark-ringis empty. It deactivates the mark.The return value is not meaningful.
This variable, if non-
nil, enables Transient Mark mode. In Transient Mark mode, every buffer-modifying primitive setsdeactivate-mark. As a consequence, most commands that modify the buffer also deactivate the mark.When Transient Mark mode is enabled and the mark is active, many commands that normally apply to the text near point instead apply to the region. Such commands should use the function
use-region-pto test whether they should operate on the region. See The Region.Lisp programs can set
transient-mark-modeto non-nil, non-tvalues to enable Transient Mark mode temporarily. If the value islambda, Transient Mark mode is automatically turned off after any action, such as buffer modification, that would normally deactivate the mark. If the value is(only .oldval), thentransient-mark-modeis set to the value oldval after any subsequent command that moves point and is not shift-translated (see shift-translation), or after any other action that would normally deactivate the mark.
If this is non-
nil, Lisp programs and the Emacs user can use the mark even when it is inactive. This option affects the behavior of Transient Mark mode. When the option is non-nil, deactivation of the mark turns off region highlighting, but commands that use the mark behave as if the mark were still active.
If an editor command sets this variable non-
nil, then the editor command loop deactivates the mark after the command returns (if Transient Mark mode is enabled). All the primitives that change the buffer setdeactivate-mark, to deactivate the mark when the command is finished.To write Lisp code that modifies the buffer without causing deactivation of the mark at the end of the command, bind
deactivate-marktonilaround the code that does the modification. For example:(let (deactivate-mark) (insert " "))
If Transient Mark mode is enabled or force is non-
nil, this function deactivates the mark and runs the normal hookdeactivate-mark-hook. Otherwise, it does nothing.
The mark is active when this variable is non-
nil. This variable is always buffer-local in each buffer. Do not use the value of this variable to decide whether a command that normally operates on text near point should operate on the region instead. Use the functionuse-region-pfor that (see The Region).
These normal hooks are run, respectively, when the mark becomes active and when it becomes inactive. The hook
activate-mark-hookis also run at the end of a command if the mark is active and it is possible that the region may have changed.
This function implements the “shift-selection” behavior of point-motion commands. See Shift Selection. It is called automatically by the Emacs command loop whenever a command with a ‘^’ character in its
interactivespec is invoked, before the command itself is executed (see ^).If
shift-select-modeis non-niland the current command was invoked via shift translation (see shift-translation), this function sets the mark and temporarily activates the region, unless the region was already temporarily activated in this way. Otherwise, if the region has been activated temporarily, it deactivates the mark and restores the variabletransient-mark-modeto its earlier value.
The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first.
mark-ring ⇒ (#<marker at 11050 in markers.texi> #<marker at 10832 in markers.texi> ...)
The value of this variable is the maximum size of
mark-ring. If more marks than this are pushed onto themark-ring,push-markdiscards an old mark when it adds a new one.
The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.
The next two functions signal an error if the mark does not point
anywhere. If Transient Mark mode is enabled and
mark-even-if-inactive is nil, they also signal an error
if the mark is inactive.
This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller.
This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger.
Few programs need to use the region-beginning and
region-end functions. A command designed to operate on a region
should normally use interactive with the ‘r’ specification
to find the beginning and end of the region. This lets other Lisp
programs specify the bounds explicitly as arguments. (See Interactive Codes.)
This function returns
tif Transient Mark mode is enabled, the mark is active, and there's a valid region in the buffer. Commands that operate on the region (instead of on text near point) when there's an active mark should use this to test whether to do that.
This chapter describes the functions that deal with the text in a buffer. Most examine, insert, or delete text in the current buffer, often operating at point or on text adjacent to point. Many are interactive. All the functions that change the text provide for undoing the changes (see Undo).
Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named start and end.
These arguments should be either markers (see Markers) or numeric
character positions (see Positions). The order of these arguments
does not matter; it is all right for start to be the end of the
region and end the beginning. For example, (delete-region 1
10) and (delete-region 10 1) are equivalent. An
args-out-of-range error is signaled if either start or
end is outside the accessible portion of the buffer. In an
interactive call, point and the mark are used for these arguments.
Throughout this chapter, “text” refers to the characters in the buffer, together with their properties (when relevant). Keep in mind that point is always between two characters, and the cursor appears on the character after point.
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in Regexp Search.
In the following four functions, “beginning” or “end” of buffer refers to the beginning or end of the accessible portion.
This function returns the character in the current buffer at (i.e., immediately after) position position. If position is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is
nil. The default for position is point.In the following example, assume that the first character in the buffer is ‘@’:
(string (char-after 1)) ⇒ "@"
This function returns the character in the current buffer immediately before position position. If position is out of range for this purpose, either at or before the beginning of the buffer, or beyond the end, then the value is
nil. The default for position is point.
This function returns the character following point in the current buffer. This is similar to
(char-after (point)). However, if point is at the end of the buffer, thenfollowing-charreturns 0.Remember that point is always between characters, and the cursor normally appears over the character following point. Therefore, the character returned by
following-charis the character the cursor is over.In this example, point is between the ‘a’ and the ‘c’.
---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (string (preceding-char)) ⇒ "a" (string (following-char)) ⇒ "c"
This function returns the character preceding point in the current buffer. See above, under
following-char, for an example. If point is at the beginning of the buffer,preceding-charreturns 0.
This function returns
tif point is at the beginning of the buffer. If narrowing is in effect, this means the beginning of the accessible portion of the text. See alsopoint-minin Point.
This function returns
tif point is at the end of the buffer. If narrowing is in effect, this means the end of accessible portion of the text. See alsopoint-maxin See Point.
This function returns
tif point is at the beginning of a line. See Text Lines. The beginning of the buffer (or of its accessible portion) always counts as the beginning of a line.
This function returns
tif point is at the end of a line. The end of the buffer (or of its accessible portion) is always considered the end of a line.
This section describes functions that allow a Lisp program to convert any portion of the text in the buffer into a string.
This function returns a string containing a copy of the text of the region defined by positions start and end in the current buffer. If the arguments are not positions in the accessible portion of the buffer,
buffer-substringsignals anargs-out-of-rangeerror.It is not necessary for start to be less than end; the arguments can be given in either order. But most often the smaller argument is written first.
Here's an example which assumes Font-Lock mode is not enabled:
---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) ⇒ "This is t" (buffer-substring (point-max) 10) ⇒ "he contents of buffer foo\n"If the text being copied has any text properties, these are copied into the string along with the characters they belong to. See Text Properties. However, overlays (see Overlays) in the buffer and their properties are ignored, not copied.
For example, if Font-Lock mode is enabled, you might get results like these:
(buffer-substring 1 10) ⇒ #("This is t" 0 1 (fontified t) 1 9 (fontified t))
This is like
buffer-substring, except that it does not copy text properties, just the characters themselves. See Text Properties.
This function passes the buffer text between start and end through the filter functions specified by the variable
buffer-substring-filters, and returns the value from the last filter function. Ifbuffer-substring-filtersisnil, the value is the unaltered text from the buffer, whatbuffer-substringwould return.If delete is non-
nil, this function deletes the text between start and end after copying it, likedelete-and-extract-region.If noprops is non-
nil, the final string returned does not include text properties, while the string passed through the filters still includes text properties from the buffer text.Lisp code should use this function instead of
buffer-substring,buffer-substring-no-properties, ordelete-and-extract-regionwhen copying into user-accessible data structures such as the kill-ring, X clipboard, and registers. Major and minor modes can add functions tobuffer-substring-filtersto alter such text as it is copied out of the buffer.
This variable should be a list of functions that accept a single argument, a string, and return a string.
filter-buffer-substringpasses the buffer substring to the first function in this list, and the return value of each function is passed to the next function. The return value of the last function is used as the return value offilter-buffer-substring.As a special convention, point is set to the start of the buffer text being operated on (i.e., the start argument for
filter-buffer-substring) before these functions are called.If this variable is
nil, no filtering is performed.
This function returns the contents of the entire accessible portion of the current buffer as a string. It is equivalent to
(buffer-substring (point-min) (point-max))---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-string) ⇒ "This is the contents of buffer foo\n"
This function returns the symbol (or word) at or near point, as a string. The return value includes no text properties.
If the optional argument really-word is non-
nil, it finds a word; otherwise, it finds a symbol (which includes both word characters and symbol constituent characters).If the optional argument strict is non-
nil, then point must be in or next to the symbol or word—if no symbol or word is there, the function returnsnil. Otherwise, a nearby symbol or word on the same line is acceptable.
Return the thing around or next to point, as a string.
The argument thing is a symbol which specifies a kind of syntactic entity. Possibilities include
symbol,list,sexp,defun,filename,url,word,sentence,whitespace,line,page, and others.---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (thing-at-point 'word) ⇒ "Peace" (thing-at-point 'line) ⇒ "Gentlemen may cry ``Peace! Peace!,''\n" (thing-at-point 'whitespace) ⇒ nil
This function lets you compare portions of the text in a buffer, without copying them into strings first.
This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer (or a buffer name) and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use
nilfor buffer1, buffer2, or both to stand for the current buffer.The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings.
This function ignores case when comparing characters if
case-fold-searchis non-nil. It always ignores text properties.Suppose the current buffer contains the text ‘foobarbar haha!rara!’; then in this example the two substrings are ‘rbar ’ and ‘rara!’. The value is 2 because the first substring is greater at the second character.
(compare-buffer-substrings nil 6 11 nil 16 21) ⇒ 2
Insertion means adding new text to a buffer. The inserted text goes at point—between the character before point and the character after point. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion after point and the latter insertion before point.
Insertion relocates markers that point at positions after the
insertion point, so that they stay with the surrounding text
(see Markers). When a marker points at the place of insertion,
insertion may or may not relocate the marker, depending on the marker's
insertion type (see Marker Insertion Types). Certain special
functions such as insert-before-markers relocate all such markers
to point after the inserted text, regardless of the markers' insertion
type.
Insertion functions signal an error if the current buffer is read-only or if they insert within read-only text.
These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa—if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See Converting Representations.
This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all args are either strings or characters. The value is
nil.
This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. An error is signaled unless all args are either strings or characters. The value is
nil.This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. If an overlay begins at the insertion point, the inserted text falls outside the overlay; if a nonempty overlay ends at the insertion point, the inserted text falls inside that overlay.
This function inserts count instances of character into the current buffer before point. The argument count should be an integer, and character must be a character. The value is
nil.This function does not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See Converting Representations.
If inherit is non-
nil, then the inserted characters inherit sticky text properties from the two characters before and after the insertion point. See Sticky Properties.
This function inserts a portion of buffer from-buffer-or-name (which must already exist) into the current buffer before point. The text inserted is the region between start and end. (These arguments default to the beginning and end of the accessible portion of that buffer.) This function returns
nil.In this example, the form is executed with buffer ‘bar’ as the current buffer. We assume that buffer ‘bar’ is initially empty.
---------- Buffer: foo ---------- We hold these truths to be self-evident, that all ---------- Buffer: foo ---------- (insert-buffer-substring "foo" 1 20) ⇒ nil ---------- Buffer: bar ---------- We hold these truth-!- ---------- Buffer: bar ----------
This is like
insert-buffer-substringexcept that it does not copy any text properties.
See Sticky Properties, for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties.
This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.
This command inserts the entire accessible contents of from-buffer-or-name (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is
nil.
This command inserts the last character typed; it does so count times, before point, and returns
nil. Most printing characters are bound to this command. In routine use,self-insert-commandis the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap.In an interactive call, count is the numeric prefix argument.
Self-insertion translates the input character through
translation-table-for-input. See Translation of Characters.This command calls
auto-fill-functionwhenever that is non-niland the character inserted is in the tableauto-fill-chars(see Auto Filling).This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See Abbrevs, and Syntax Class Table.) It is also responsible for calling
blink-paren-functionwhen the inserted character has close parenthesis syntax (see Blinking).Do not try substituting your own definition of
self-insert-commandfor the standard one. The editor command loop handles this function specially.
This command inserts newlines into the current buffer before point. If number-of-newlines is supplied, that many newline characters are inserted.
This function calls
auto-fill-functionif the current column number is greater than the value offill-columnand number-of-newlines isnil. Typically whatauto-fill-functiondoes is insert a newline; thus, the overall result in this case is to insert two newlines at different places: one at point, and another earlier in the line.newlinedoes not auto-fill if number-of-newlines is non-nil.This command indents to the left margin if that is not zero. See Margins.
The value returned is
nil. In an interactive call, count is the numeric prefix argument.
This variable controls whether overwrite mode is in effect. The value should be
overwrite-mode-textual,overwrite-mode-binary, ornil.overwrite-mode-textualspecifies textual overwrite mode (treats newlines and tabs specially), andoverwrite-mode-binaryspecifies binary overwrite mode (treats newlines and tabs like any other characters).
Deletion means removing part of the text in a buffer, without saving it in the kill ring (see The Kill Ring). Deleted text can't be yanked, but can be reinserted using the undo mechanism (see Undo). Some deletion functions do save text in the kill ring in some special cases.
All of the deletion functions operate on the current buffer.
This function deletes the entire text of the current buffer (not just the accessible portion), leaving it empty. If the buffer is read-only, it signals a
buffer-read-onlyerror; if some of the text in it is read-only, it signals atext-read-onlyerror. Otherwise, it deletes the text without asking for any confirmation. It returnsnil.Normally, deleting a large amount of text from a buffer inhibits further auto-saving of that buffer “because it has shrunk.” However,
erase-bufferdoes not do this, the idea being that the future text is not really related to the former text, and its size should not be compared with that of the former text.
This command deletes the text between positions start and end in the current buffer, and returns
nil. If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.
This function deletes the text between positions start and end in the current buffer, and returns a string containing the text just deleted.
If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.
This command deletes count characters directly after point, or before point if count is negative. If killp is non-
nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This command deletes count characters directly before point, or after point if count is negative. If killp is non-
nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This command deletes count characters backward, changing tabs into spaces. When the next character to be deleted is a tab, it is first replaced with the proper number of spaces to preserve alignment and then one of those spaces is deleted instead of the tab. If killp is non-
nil, then the command saves the deleted characters in the kill ring.Conversion of tabs to spaces happens only if count is positive. If it is negative, exactly −count characters after point are deleted.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This option specifies how
backward-delete-char-untabifyshould deal with whitespace. Possible values includeuntabify, the default, meaning convert a tab to many spaces and delete one;hungry, meaning delete all tabs and spaces before point with one command;allmeaning delete all tabs, spaces and newlines before point, andnil, meaning do nothing special for whitespace characters.
This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.
This function deletes all spaces and tabs around point. It returns
nil.If backward-only is non-
nil, the function deletes spaces and tabs before point, but not after point.In the following examples, we call
delete-horizontal-spacefour times, once on each line, with point between the second and third characters on the line each time.---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. ⇒ nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ----------
This function joins the line point is on to the previous line, deleting any whitespace at the join and in some cases replacing it with one space. If join-following-p is non-
nil,delete-indentationjoins this line to the following line instead. The function returnsnil.If there is a fill prefix, and the second of the lines being joined starts with the prefix, then
delete-indentationdeletes the fill prefix before joining the lines. See Margins.In the example below, point is located on the line starting ‘events’, and it makes no difference if there are trailing spaces in the preceding line.
---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) ⇒ nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ----------After the lines are joined, the function
fixup-whitespaceis responsible for deciding whether to leave a space at the junction.
This function replaces all the horizontal whitespace surrounding point with either one space or no space, according to the context. It returns
nil.At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. See Syntax Class Table.
In the example below,
fixup-whitespaceis called the first time with point before the word ‘spaces’ in the first line. For the second invocation, point is directly after the ‘(’.---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) ⇒ nil (fixup-whitespace) ⇒ nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ----------
This command replaces any spaces and tabs around point with a single space, or n spaces if n is specified. It returns
nil.
This function deletes blank lines surrounding point. If point is on a blank line with one or more blank lines before or after it, then all but one of them are deleted. If point is on an isolated blank line, then it is deleted. If point is on a nonblank line, the command deletes all blank lines immediately following it.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-linesreturnsnil.
Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have ‘kill-’ in their name. By contrast, the functions whose names start with ‘delete-’ normally do not save text for yanking (though they can still be undone); these are “deletion” functions.
Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to delete text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See Deletion.
Killed text is saved for later yanking in the kill ring. This
is a list that holds a number of recent kills, not just the last text
kill. We call this a “ring” because yanking treats it as having
elements in a cyclic order. The list is kept in the variable
kill-ring, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.
Some people think this use of the word “kill” is unfortunate, since it refers to operations that specifically do not destroy the entities “killed.” This is in sharp contrast to ordinary life, in which death is permanent and “killed” entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term “cut ring” makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now.
The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this:
("some text" "a different piece of text" "even older text")
When the list reaches kill-ring-max entries in length, adding a
new entry automatically deletes the last entry.
When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single kill ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one.
For yanking, one entry in the kill ring is designated the “front” of the ring. Some yank commands “rotate” the ring by designating a different element as the “front.” But this virtual rotation doesn't change the list itself—the most recent entry always comes first in the list.
kill-region is the usual subroutine for killing text. Any
command that calls this function is a “kill command” (and should
probably have ‘kill’ in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element. It determines automatically (using
last-command) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.
This function kills the text in the region defined by start and end. The text is deleted but saved in the kill ring, along with its text properties. The value is always
nil.In an interactive call, start and end are point and the mark.
If the buffer or text is read-only,
kill-regionmodifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use a series of kill commands to copy text from a read-only buffer into the kill ring.
If this option is non-
nil,kill-regiondoes not signal an error if the buffer or text is read-only. Instead, it simply returns, updating the kill ring but not changing the buffer.
This command saves the region defined by start and end on the kill ring (including text properties), but does not delete the text from the buffer. It returns
nil.The command does not set
this-commandtokill-region, so a subsequent kill command does not append to the same kill ring entry.In Lisp programs, it is better to use
kill-neworkill-appendinstead of this command. See Low-Level Kill Ring.
Yanking means inserting text from the kill ring, but it does
not insert the text blindly. Yank commands and some other commands
use insert-for-yank to perform special processing on the
text that they copy into the buffer.
This function normally works like
insertexcept that it doesn't insert the text properties in theyank-excluded-propertieslist. However, if any part of string has a non-nilyank-handlertext property, that property can do various special processing on that part of the text being inserted.
This function resembles
insert-buffer-substringexcept that it doesn't insert the text properties in theyank-excluded-propertieslist.
You can put a yank-handler text property on all or part of
the text to control how it will be inserted if it is yanked. The
insert-for-yank function looks for that property. The property
value must be a list of one to four elements, with the following
format (where elements after the first may be omitted):
(function param noexclude undo)
Here is what the elements do:
nil, it is called instead of
insert to insert the string. function takes one
argument—the string to insert.
nil, it replaces string
(or the part of string being processed) as the object passed to
function (or insert); for example, if function is
yank-rectangle, param should be a list of strings to
insert as a rectangle.
nil, the normal removal of the
yank-excluded-properties is not performed; instead function is
responsible for removing those properties. This may be necessary
if function adjusts point before or after inserting the object.
nil, it is a function that will be
called by yank-pop to undo the insertion of the current object.
It is called with two arguments, the start and end of the current
region. function can set yank-undo-function to override
the undo value.
This section describes higher-level commands for yanking, which are
intended primarily for the user but useful also in Lisp programs.
Both yank and yank-pop honor the
yank-excluded-properties variable and yank-handler text
property (see Yanking).
This command inserts before point the text at the front of the kill ring. It sets the mark at the beginning of that text, using
push-mark(see The Mark), and puts point at the end.If arg is a non-
nillist (which occurs interactively when the user types C-u with no digits), thenyankinserts the text as described above, but puts point before the yanked text and sets the mark after it.If arg is a number, then
yankinserts the argth most recently killed text—the argth element of the kill ring list, counted cyclically from the front, which is considered the first element for this purpose.
yankdoes not alter the contents of the kill ring, unless it used text provided by another program, in which case it pushes that text onto the kill ring. However if arg is an integer different from one, it rotates the kill ring to place the yanked string at the front.
yankreturnsnil.
This command replaces the just-yanked entry from the kill ring with a different entry from the kill ring.
This is allowed only immediately after a
yankor anotheryank-pop. At such a time, the region contains text that was just inserted by yanking.yank-popdeletes that text and inserts in its place a different piece of killed text. It does not add the deleted text to the kill ring, since it is already in the kill ring somewhere. It does however rotate the kill ring to place the newly yanked string at the front.If arg is
nil, then the replacement text is the previous element of the kill ring. If arg is numeric, the replacement is the argth previous kill. If arg is negative, a more recent kill is the replacement.The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest.
The return value is always
nil.
If this variable is non-
nil, the functionyank-popuses its value instead ofdelete-regionto delete the text inserted by the previousyankoryank-popcommand. The value must be a function of two arguments, the start and end of the current region.The function
insert-for-yankautomatically sets this variable according to the undo element of theyank-handlertext property, if there is one.
These functions and variables provide access to the kill ring at a lower level, but are still convenient for use in Lisp programs, because they take care of interaction with window system selections (see Window System Selections).
The function
current-killrotates the yanking pointer, which designates the “front” of the kill ring, by n places (from newer kills to older ones), and returns the text at that place in the ring.If the optional second argument do-not-move is non-
nil, thencurrent-killdoesn't alter the yanking pointer; it just returns the nth kill, counting from the current yanking pointer.If n is zero, indicating a request for the latest kill,
current-killcalls the value ofinterprogram-paste-function(documented below) before consulting the kill ring. If that value is a function and calling it returns a string or a list of several string,current-killpushes the strings onto the kill ring and returns the first string. It also sets the yanking pointer to point to the kill-ring entry of the first string returned byinterprogram-paste-function, regardless of the value of do-not-move. Otherwise,current-killdoes not treat a zero value for n specially: it returns the entry pointed at by the yanking pointer and does not move the yanking pointer.
This function pushes the text string onto the kill ring and makes the yanking pointer point to it. It discards the oldest entry if appropriate. It also invokes the value of
interprogram-cut-function(see below).If replace is non-
nil, thenkill-newreplaces the first element of the kill ring with string, rather than pushing string onto the kill ring.
This function appends the text string to the first entry in the kill ring and makes the yanking pointer point to the combined entry. Normally string goes at the end of the entry, but if before-p is non-
nil, it goes at the beginning. This function also invokes the value ofinterprogram-cut-function(see below).
This variable provides a way of transferring killed text from other programs, when you are using a window system. Its value should be
nilor a function of no arguments.If the value is a function,
current-killcalls it to get the “most recent kill.” If the function returns a non-nilvalue, then that value is used as the “most recent kill.” If it returnsnil, then the front of the kill ring is used.To facilitate support for window systems that support multiple selections, this function may also return a list of strings. In that case, the first string is used as the “most recent kill”, and all the other strings are pushed onto the kill ring, for easy access by
yank-pop.The normal use of this function is to get the window system's primary selection as the most recent kill, even if the selection belongs to another application. See Window System Selections. However, if the selection was provided by the current Emacs session, this function should return
nil. (If it is hard to tell whether Emacs or some other program provided the selection, it should be good enough to usestring=to compare it with the last text Emacs provided.)
This variable provides a way of communicating killed text to other programs, when you are using a window system. Its value should be
nilor a function of one required and one optional argument.If the value is a function,
kill-newandkill-appendcall it with the new first element of the kill ring as the first argument. The second, optional, argument has the same meaning as the push argument tox-set-cut-buffer(see Definition of x-set-cut-buffer) and only affects the second and later cut buffers.The normal use of this function is to set the window system's primary selection (and first cut buffer) from the newly killed text. See Window System Selections.
The variable kill-ring holds the kill ring contents, in the
form of a list of strings. The most recent kill is always at the front
of the list.
The kill-ring-yank-pointer variable points to a link in the
kill ring list, whose car is the text to yank next. We say it
identifies the “front” of the ring. Moving
kill-ring-yank-pointer to a different link is called
rotating the kill ring. We call the kill ring a “ring” because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa. Rotation of the kill ring is
virtual; it does not change the value of kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp
variables whose values are normally lists. The word “pointer” in the
name of the kill-ring-yank-pointer indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.
The value of kill-ring-yank-pointer is always eq to one
of the links in the kill ring list. The element it identifies is the
car of that link. Kill commands, which change the kill ring, also
set this variable to the value of kill-ring. The effect is to
rotate the ring so that the newly killed text is at the front.
Here is a diagram that shows the variable kill-ring-yank-pointer
pointing to the second entry in the kill ring ("some text" "a
different piece of text" "yet older text").
kill-ring ---- kill-ring-yank-pointer
| |
| v
| --- --- --- --- --- ---
--> | | |------> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| | -->"yet older text"
| |
| --> "a different piece of text"
|
--> "some text"
This state of affairs might occur after C-y (yank)
immediately followed by M-y (yank-pop).
This variable holds the list of killed text sequences, most recently killed first.
This variable's value indicates which element of the kill ring is at the “front” of the ring for yanking. More precisely, the value is a tail of the value of
kill-ring, and its car is the kill string that C-y should yank.
The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for
kill-ring-maxis 60.
Most buffers have an undo list, which records all changes made
to the buffer's text so that they can be undone. (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful. In particular, any buffer whose
name begins with a space has its undo recording off by default;
see Buffer Names.) All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable buffer-undo-list.
This buffer-local variable's value is the undo list of the current buffer. A value of
tdisables the recording of undo information.
Here are the kinds of elements an undo list can have:
(beg . end)(text . position)(abs position). If position is
positive, point was at the beginning of the deleted text, otherwise it
was at the end.
(t high . low)primitive-undo uses those
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's modification time matches those numbers.
(nil property value beg . end)(put-text-property beg end property value)
(marker . adjustment)(apply funname . args)(apply delta beg end funname . args)This kind of element enables undo limited to a region to determine
whether the element pertains to that region.
nilThis function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns
nil.The editor command loop automatically calls
undo-boundaryjust before executing each key sequence, so that each undo normally undoes the effects of one command. As an exception, the commandself-insert-command, which produces self-inserting input characters (see Commands for Insertion), may remove the boundary inserted by the command loop: a boundary is accepted for the first such character, the next 19 consecutive self-inserting input characters do not have boundaries, and then the 20th does; and so on as long as the self-inserting characters continue. Hence, sequences of consecutive character insertions can be undone as a group.All buffer modifications add a boundary whenever the previous undoable change was made in some other buffer. This is to ensure that each command makes a boundary in each buffer where it makes changes.
Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example,
query-replacecallsundo-boundaryafter each replacement, so that the user can undo individual replacements one by one.
This variable is normally
nil, but the undo commands bind it tot. This is so that various kinds of change hooks can tell when they're being called for the sake of undoing.
This is the basic function for undoing elements of an undo list. It undoes the first count elements of list, returning the rest of list.
primitive-undoadds elements to the buffer's undo list when it changes the buffer. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing are not part of this saved value, so they don't interfere with continuing to undo.This function does not bind
undo-in-progress.
This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
buffer-undo-list yourself.
This command enables recording undo information for buffer buffer-or-name, so that subsequent changes can be undone. If no argument is supplied, then the current buffer is used. This function does nothing if undo recording is already enabled in the buffer. It returns
nil.In an interactive call, buffer-or-name is the current buffer. You cannot specify any other buffer.
This function discards the undo list of buffer-or-name, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of buffer-or-name is already disabled, this function has no effect.
This function returns
nil.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the “size”
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Three variables control the range of acceptable
sizes: undo-limit, undo-strong-limit and
undo-outer-limit. In these variables, size is counted as the
number of bytes occupied, which includes both saved text and other
data.
This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept.
This is the upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all older change groups). There is one exception: the very latest change group is only discarded if it exceeds
undo-outer-limit.
If at garbage collection time the undo info for the current command exceeds this limit, Emacs discards the info and displays a warning. This is a last ditch limit to prevent memory overflow.
If this variable is non-
nil, when the undo info exceedsundo-outer-limit, Emacs asks in the echo area whether to discard the info. The default value isnil, which means to discard it automatically.This option is mainly intended for debugging. Garbage collection is inhibited while the question is asked, which means that Emacs might leak memory if the user waits too long before answering the question.
Filling means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be justified, which means
inserting spaces to make the left and/or right margins line up
precisely. The width is controlled by the variable fill-column.
For ease of reading, lines should be no longer than 70 or so columns.
You can use Auto Fill mode (see Auto Filling) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly.
Most of the commands in this section return values that are not
meaningful. All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(see Margins). If the current justification style is
none, the filling functions don't actually do anything.
Several of the filling functions have an argument justify.
If it is non-nil, that requests some kind of justification. It
can be left, right, full, or center, to
request a specific style of justification. If it is t, that
means to use the current justification style for this part of the text
(see current-justification, below). Any other value is treated
as full.
When you call the filling functions interactively, using a prefix
argument implies the value full for justify.
This command fills the paragraph at or after point. If justify is non-
nil, each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. See Paragraphs.When region is non-
nil, then if Transient Mark mode is enabled and the mark is active, this command callsfill-regionto fill all the paragraphs in the region, instead of filling only the current paragraph. When this command is called interactively, region ist.
This command fills each of the paragraphs in the region from start to end. It justifies as well if justify is non-
nil.If nosqueeze is non-
nil, that means to leave whitespace other than line breaks untouched. If to-eop is non-nil, that means to keep filling to the end of the paragraph—or the next hard newline, ifuse-hard-newlinesis enabled (see below).The variable
paragraph-separatecontrols how to distinguish paragraphs. See Standard Regexps.
This command fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph were indented with spaces, the filled paragraph will remain indented in the same fashion.
The first two arguments, start and end, are the beginning and end of the region to be filled. The third and fourth arguments, justify and citation-regexp, are optional. If justify is non-
nil, the paragraphs are justified as well as filled. If citation-regexp is non-nil, it means the function is operating on a mail message and therefore should not fill the header lines. If citation-regexp is a string, it is used as a regular expression; if it matches the beginning of a line, that line is treated as a citation marker.Ordinarily,
fill-individual-paragraphsregards each change in indentation as starting a new paragraph. Iffill-individual-varying-indentis non-nil, then only separator lines separate paragraphs. That mode can handle indented paragraphs with additional indentation on the first line.
This variable alters the action of
fill-individual-paragraphsas described above.
This command considers a region of text as a single paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when justify is non-
nil.If nosqueeze is non-
nil, that means to leave whitespace other than line breaks untouched. If squeeze-after is non-nil, it specifies a position in the region, and means don't canonicalize spaces before that position.In Adaptive Fill mode, this command calls
fill-context-prefixto choose a fill prefix by default. See Adaptive Fill.
This command inserts spaces between the words of the current line so that the line ends exactly at
fill-column. It returnsnil.The argument how, if non-
nilspecifies explicitly the style of justification. It can beleft,right,full,center, ornone. If it ist, that means to do follow specified justification style (seecurrent-justification, below).nilmeans to do full justification.If eop is non-
nil, that means do only left-justification ifcurrent-justificationspecifies full justification. This is used for the last line of a paragraph; even if the paragraph as a whole is fully justified, the last line should not be.If nosqueeze is non-
nil, that means do not change interior whitespace.
This variable's value specifies the style of justification to use for text that doesn't specify a style with a text property. The possible values are
left,right,full,center, ornone. The default value isleft.
This function returns the proper justification style to use for filling the text around point.
This returns the value of the
justificationtext property at point, or the variable default-justification if there is no such text property. However, it returnsnilrather thannoneto mean “don't justify”.
If this variable is non-
nil, a period followed by just one space does not count as the end of a sentence, and the filling functions avoid breaking the line at such a place.
If this variable is non-
nil, a sentence can end without a period. This is used for languages like Thai, where sentences end with a double space but without a period.
If this variable is non-
nil, it should be a string of characters that can end a sentence without following spaces.
This variable provides a way to override the filling of paragraphs. If its value is non-
nil,fill-paragraphcalls this function to do the work. If the function returns a non-nilvalue,fill-paragraphassumes the job is done, and immediately returns that value.The usual use of this feature is to fill comments in programming language modes. If the function needs to fill a paragraph in the usual way, it can do so as follows:
(let ((fill-paragraph-function nil)) (fill-paragraph arg))
This variable provides a way to override how the filling functions, such as
fill-regionandfill-paragraph, move forward to the next paragraph. Its value should be a function, which is called with a single argument n, the number of paragraphs to move, and should return the difference between n and the number of paragraphs actually moved. The default value of this variable isforward-paragraph. See Paragraphs.
If this variable is non-
nil, the filling functions do not delete newlines that have thehardtext property. These “hard newlines” act as paragraph separators.
This buffer-local variable, if non-
nil, specifies a string of text that appears at the beginning of normal text lines and should be disregarded when filling them. Any line that fails to start with the fill prefix is considered the start of a paragraph; so is any line that starts with the fill prefix followed by additional whitespace. Lines that start with the fill prefix but no additional whitespace are ordinary text lines that can be filled together. The resulting filled lines also start with the fill prefix.The fill prefix follows the left margin whitespace, if any.
This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification, and centering commands are affected by this variable, including Auto Fill mode (see Auto Filling).
As a practical matter, if you are writing text for other people to read, you should set
fill-columnto no more than 70. Otherwise the line will be too long for people to read comfortably, and this can make the text seem clumsy.The default value for
fill-columnis 70.
This sets the
left-marginproperty on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
This sets the
right-marginproperty on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
This function returns the proper left margin value to use for filling the text around point. The value is the sum of the
left-marginproperty of the character at the start of the current line (or zero if none), and the value of the variableleft-margin.
This function returns the proper fill column value to use for filling the text around point. The value is the value of the
fill-columnvariable, minus the value of theright-marginproperty of the character after point.
This function moves point to the left margin of the current line. The column moved to is determined by calling the function
current-left-margin. If the argument n is non-nil,move-to-left-marginmoves forward n−1 lines first.If force is non-
nil, that says to fix the line's indentation if that doesn't match the left margin value.
This function removes left margin indentation from the text between from and to. The amount of indentation to delete is determined by calling
current-left-margin. In no case does this function delete non-whitespace. If from and to are omitted, they default to the whole buffer.
This function adjusts the indentation at the beginning of the current line to the value specified by the variable
left-margin. (That may involve either inserting or deleting whitespace.) This function is value ofindent-line-functionin Paragraph-Indent Text mode.
This variable specifies the base left margin column. In Fundamental mode, C-j indents to this column. This variable automatically becomes buffer-local when set in any fashion.
This variable gives major modes a way to specify not to break a line at certain places. Its value should be a list of functions. Whenever filling considers breaking the line at a certain place in the buffer, it calls each of these functions with no arguments and with point located at that place. If any of the functions returns non-
nil, then the line won't be broken there.
When Adaptive Fill Mode is enabled, Emacs determines the fill prefix automatically from the text in each paragraph being filled rather than using a predetermined value. During filling, this fill prefix gets inserted at the start of the second and subsequent lines of the paragraph as described in Filling, and in Auto Filling.
Adaptive Fill mode is enabled when this variable is non-
nil. It istby default.
This function implements the heart of Adaptive Fill mode; it chooses a fill prefix based on the text between from and to, typically the start and end of a paragraph. It does this by looking at the first two lines of the paragraph, based on the variables described below.
Usually, this function returns the fill prefix, a string. However, before doing this, the function makes a final check (not specially mentioned in the following) that a line starting with this prefix wouldn't look like the start of a paragraph. Should this happen, the function signals the anomaly by returning
nilinstead.In detail,
fill-context-prefixdoes this:
- It takes a candidate for the fill prefix from the first line—it tries first the function in
adaptive-fill-function(if any), then the regular expressionadaptive-fill-regexp(see below). The first non-nilresult of these, or the empty string if they're bothnil, becomes the first line's candidate.- If the paragraph has as yet only one line, the function tests the validity of the prefix candidate just found. The function then returns the candidate if it's valid, or a string of spaces otherwise. (see the description of
adaptive-fill-first-line-regexpbelow).- When the paragraph already has two lines, the function next looks for a prefix candidate on the second line, in just the same way it did for the first line. If it doesn't find one, it returns
nil.- The function now compares the two candidate prefixes heuristically: if the non-whitespace characters in the line 2 candidate occur in the same order in the line 1 candidate, the function returns the line 2 candidate. Otherwise, it returns the largest initial substring which is common to both candidates (which might be the empty string).
Adaptive Fill mode matches this regular expression against the text starting after the left margin whitespace (if any) on a line; the characters it matches are that line's candidate for the fill prefix.
The default value matches whitespace with certain punctuation characters intermingled.
Used only in one-line paragraphs, this regular expression acts as an additional check of the validity of the one available candidate fill prefix: the candidate must match this regular expression, or match
comment-start-skip. If it doesn't,fill-context-prefixreplaces the candidate with a string of spaces “of the same width” as it.The default value of this variable is
"\\`[ \t]*\\'", which matches only a string of whitespace. The effect of this default is to force the fill prefixes found in one-line paragraphs always to be pure whitespace.
You can specify more complex ways of choosing a fill prefix automatically by setting this variable to a function. The function is called with point after the left margin (if any) of a line, and it must preserve point. It should return either “that line's” fill prefix or
nil, meaning it has failed to determine a prefix.
Auto Fill mode is a minor mode that fills lines automatically as text is inserted. This section describes the hook used by Auto Fill mode. For a description of functions that you can call explicitly to fill and justify existing text, see Filling.
Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See Margins.
The value of this buffer-local variable should be a function (of no arguments) to be called after self-inserting a character from the table
auto-fill-chars. It may benil, in which case nothing special is done in that case.The value of
auto-fill-functionisdo-auto-fillwhen Auto-Fill mode is enabled. That is a function whose sole purpose is to implement the usual strategy for breaking a line.In older Emacs versions, this variable was namedauto-fill-hook, but since it is not called with the standard convention for hooks, it was renamed toauto-fill-functionin version 19.
This variable specifies the function to use for
auto-fill-function, if and when Auto Fill is turned on. Major modes can set buffer-local values for this variable to alter how Auto Fill works.
A char table of characters which invoke
auto-fill-functionwhen self-inserted—space and newline in most language environments. They have an entrytin the table.
The sorting functions described in this section all rearrange text in
a buffer. This is in contrast to the function sort, which
rearranges the order of the elements of a list (see Rearrangement).
The values returned by these functions are not meaningful.
This function is the general text-sorting routine that subdivides a buffer into records and then sorts them. Most of the commands in this section use this function.
To understand how
sort-subrworks, consider the whole accessible portion of the buffer as being divided into disjoint pieces called sort records. The records may or may not be contiguous, but they must not overlap. A portion of each sort record (perhaps all of it) is designated as the sort key. Sorting rearranges the records in order by their sort keys.Usually, the records are rearranged in order of ascending sort key. If the first argument to the
sort-subrfunction, reverse, is non-nil, the sort records are rearranged in order of descending sort key.The next four arguments to
sort-subrare functions that are called to move point across a sort record. They are called many times from withinsort-subr.
- nextrecfun is called with point at the end of a record. This function moves point to the start of the next record. The first record is assumed to start at the position of point when
sort-subris called. Therefore, you should usually move point to the beginning of the buffer before callingsort-subr.This function can indicate there are no more sort records by leaving point at the end of the buffer.
- endrecfun is called with point within a record. It moves point to the end of the record.
- startkeyfun is called to move point from the start of a record to the start of the sort key. This argument is optional; if it is omitted, the whole record is the sort key. If supplied, the function should either return a non-
nilvalue to be used as the sort key, or returnnilto indicate that the sort key is in the buffer starting at point. In the latter case, endkeyfun is called to find the end of the sort key.- endkeyfun is called to move point from the start of the sort key to the end of the sort key. This argument is optional. If startkeyfun returns
niland this argument is omitted (ornil), then the sort key extends to the end of the record. There is no need for endkeyfun if startkeyfun returns a non-nilvalue.The argument predicate is the function to use to compare keys. If keys are numbers, it defaults to
<; otherwise it defaults tostring<.As an example of
sort-subr, here is the complete function definition forsort-lines:;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user. (defun sort-lines (reverse beg end) "Sort lines in region alphabetically;\ argument means descending order. Called from a program, there are three arguments: REVERSE (non-nil means reverse order),\ BEG and END (region to sort). The variable `sort-fold-case' determines\ whether alphabetic case affects the sort order." (interactive "P\nr") (save-excursion (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (let ((inhibit-field-text-motion t)) (sort-subr reverse 'forward-line 'end-of-line)))))Here
forward-linemoves point to the start of the next record, andend-of-linemoves point to the end of record. We do not pass the arguments startkeyfun and endkeyfun, because the entire record is used as the sort key.The
sort-paragraphsfunction is very much the same, except that itssort-subrcall looks like this:(sort-subr reverse (function (lambda () (while (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1)))) 'forward-paragraph)Markers pointing into any sort records are left with no useful position after
sort-subrreturns.
If this variable is non-
nil,sort-subrand the other buffer sorting functions ignore case when comparing strings.
This command sorts the region between start and end alphabetically as specified by record-regexp and key-regexp. If reverse is a negative integer, then sorting is in reverse order.
Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical character codes in the Emacs character set.
The value of the record-regexp argument specifies how to divide the buffer into sort records. At the end of each record, a search is done for this regular expression, and the text that matches it is taken as the next record. For example, the regular expression ‘^.+$’, which matches lines with at least one character besides a newline, would make each such line into a sort record. See Regular Expressions, for a description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each record is the sort key. The key-regexp could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position.
The key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own.
If key-regexp is:
- ‘\digit’
- then the text matched by the digitth ‘\(...\)’ parenthesis grouping in record-regexp is the sort key.
- ‘\&’
- then the whole record is the sort key.
- a regular expression
- then
sort-regexp-fieldssearches for a match for the regular expression within the record. If such a match is found, it is the sort key. If there is no match for key-regexp within a record then that record is ignored, which means its position in the buffer is not changed. (The other records may move around it.)For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter ‘f’, you should set record-regexp to ‘^.*$’ and set key-regexp to ‘\<f\w*\>’. The resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>" (region-beginning) (region-end))If you call
sort-regexp-fieldsinteractively, it prompts for record-regexp and key-regexp in the minibuffer.
This command alphabetically sorts lines in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command alphabetically sorts paragraphs in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command alphabetically sorts pages in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command sorts lines in the region between start and end, comparing them alphabetically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.
This command sorts lines in the region between start and end, comparing them numerically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. The specified field must contain a number in each line of the region. Numbers starting with 0 are treated as octal, and numbers starting with ‘0x’ are treated as hexadecimal.
If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.
This variable specifies the default radix for
sort-numeric-fieldsto parse numbers.
This command sorts the lines in the region between beg and end, comparing them alphabetically by a certain range of columns. The column positions of beg and end bound the range of columns to sort on.
If reverse is non-
nil, the sort is in reverse order.One unusual thing about this command is that the entire line containing position beg, and the entire line containing position end, are included in the region sorted.
Note that
sort-columnsrejects text that contains tabs, because tabs could be split across the specified columns. Use M-x untabify to convert tabs to spaces before sorting.When possible, this command actually works by calling the
sortutility program.
The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line).
These functions count each character according to the number of
columns it occupies on the screen. This means control characters count
as occupying 2 or 4 columns, depending upon the value of
ctl-arrow, and tabs count as occupying a number of columns that
depends on the value of tab-width and on the column where the tab
begins. See Usual Display.
Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0. They also ignore overlays and text properties, aside from invisibility.
This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column position is the sum of the widths of all the displayed representations of the characters between the start of the current line and point.
For an example of using
current-column, see the description ofcount-linesin Text Lines.
This function moves point to column in the current line. The calculation of column takes into account the widths of the displayed representations of the characters between the start of the line and point.
When called interactively, column is the value of prefix numeric argument. If column is not an integer, an error is signaled.
If column column is beyond the end of the line, point moves to the end of the line. If column is negative, point moves to the beginning of the line.
If it is impossible to move to column column because that is in the middle of a multicolumn character such as a tab, point moves to the end of that character. However, if force is non-
nil, and column is in the middle of a tab, thenmove-to-columnconverts the tab into spaces so that it can move precisely to column column. Other multicolumn characters can cause anomalies despite force, since there is no way to split them.The argument force also has an effect if the line isn't long enough to reach column column; if it is
t, that means to add whitespace at the end of the line to reach that column.The return value is the column number actually moved to.
The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin.
This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. See Width, for related functions.
This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line.
This function indents from point with tabs and spaces until column is reached. If minimum is specified and non-
nil, then at least that many spaces are inserted even if this requires going beyond column. Otherwise the function does nothing if point is already beyond column. The value is the column at which the inserted indentation ends.The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). See Sticky Properties.
If this variable is non-
nil, indentation functions can insert tabs as well as spaces. Otherwise, they insert only spaces. Setting this variable automatically makes it buffer-local in the current buffer.
An important function of each major mode is to customize the <TAB> key to indent properly for the language being edited. This section describes the mechanism of the <TAB> key and how to control it. The functions in this section return unpredictable values.
This variable's value is the function to be used by <TAB> (and various commands) to indent the current line. The command
indent-according-to-modedoes little more than call this function.In Lisp mode, the value is the symbol
lisp-indent-line; in C mode,c-indent-line; in Fortran mode,fortran-indent-line. The default value isindent-relative. See Auto-Indentation.
This command calls the function in
indent-line-functionto indent the current line in a way appropriate for the current major mode.
This command calls the function in
indent-line-functionto indent the current line; however, if that function isindent-to-left-margin,insert-tabis called instead. (That is a trivial command that inserts a tab character.) If rigid is non-nil, this function also rigidly indents the entire balanced expression that starts at the beginning of the current line, to reflect change in indentation of the current line.
This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode.
It does indentation by calling the current
indent-line-function. In programming language modes, this is the same thing <TAB> does, but in some text modes, where <TAB> inserts a tab,newline-and-indentindents to the column specified byleft-margin.
This command reindents the current line, inserts a newline at point, and then indents the new line (the one following the newline just inserted).
This command does indentation on both lines according to the current major mode, by calling the current value of
indent-line-function. In programming language modes, this is the same thing <TAB> does, but in some text modes, where <TAB> inserts a tab,reindent-then-newline-and-indentindents to the column specified byleft-margin.
This section describes commands that indent all the lines in the region. They return unpredictable values.
This command indents each nonblank line starting between start (inclusive) and end (exclusive). If to-column is
nil,indent-regionindents each nonblank line by calling the current mode's indentation function, the value ofindent-line-function.If to-column is non-
nil, it should be an integer specifying the number of columns of indentation; then this function gives each line exactly that much indentation, by either adding or deleting whitespace.If there is a fill prefix,
indent-regionindents each line by making it start with the fill prefix.
The value of this variable is a function that can be used by
indent-regionas a short cut. It should take two arguments, the start and end of the region. You should design the function so that it will produce the same results as indenting the lines of the region one by one, but presumably faster.If the value is
nil, there is no short cut, andindent-regionactually works line by line.A short-cut function is useful in modes such as C mode and Lisp mode, where the
indent-line-functionmust scan from the beginning of the function definition: applying it to each line would be quadratic in time. The short cut can update the scan information as it moves through the lines indenting them; this takes linear time. In a mode where indenting a line individually is fast, there is no need for a short cut.
indent-regionwith a non-nilargument to-column has a different meaning and does not use this variable.
This command indents all lines starting between start (inclusive) and end (exclusive) sideways by count columns. This “preserves the shape” of the affected region, moving it as a rigid unit. Consequently, this command is useful not only for indenting regions of unindented text, but also for indenting regions of formatted code.
For example, if count is 3, this command adds 3 columns of indentation to each of the lines beginning in the region specified.
In Mail mode, C-c C-y (
mail-yank-original) usesindent-rigidlyto indent the text copied from the message being replied to.
This is like
indent-rigidly, except that it doesn't alter lines that start within strings or comments.In addition, it doesn't alter a line if nochange-regexp matches at the beginning of the line (if nochange-regexp is non-
nil).
This section describes two commands that indent the current line based on the contents of previous lines.
This command inserts whitespace at point, extending to the same column as the next indent point of the previous nonblank line. An indent point is a non-whitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace.
If the previous nonblank line has no next indent point (i.e., none at a great enough column position),
indent-relativeeither does nothing (if unindented-ok is non-nil) or callstab-to-tab-stop. Thus, if point is underneath and to the right of the last column of a short line of text, this command ordinarily moves point to the next tab stop by inserting whitespace.The return value of
indent-relativeis unpredictable.In the following example, point is at the beginning of the second line:
This line is indented twelve spaces. -!-The quick brown fox jumped.Evaluation of the expression
(indent-relative nil)produces the following:This line is indented twelve spaces. -!-The quick brown fox jumped.In this next example, point is between the ‘m’ and ‘p’ of ‘jumped’:
This line is indented twelve spaces. The quick brown fox jum-!-ped.Evaluation of the expression
(indent-relative nil)produces the following:This line is indented twelve spaces. The quick brown fox jum -!-ped.
This command indents the current line like the previous nonblank line, by calling
indent-relativewithtas the unindented-ok argument. The return value is unpredictable.If the previous nonblank line has no indent points beyond the current column, this command does nothing.
This section explains the mechanism for user-specified “tab stops” and the mechanisms that use and set them. The name “tab stops” is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (see Usual Display). Note that the <TAB> character as input uses this tab stop feature only in a few major modes, such as Text mode. See Tab Stops.
This command inserts spaces or tabs before point, up to the next tab stop column defined by
tab-stop-list. It searches the list for an element greater than the current column number, and uses that element as the column to indent to. It does nothing if no such element is found.
This variable is the list of tab stop columns used by
tab-to-tab-stops. The elements should be integers in increasing order. The tab stop columns need not be evenly spaced.Use M-x edit-tab-stops to edit the location of tab stops interactively.
These commands, primarily for interactive use, act based on the indentation in the text.
This command moves point to the first non-whitespace character in the current line (which is the line in which point is located). It returns
nil.
This command moves point backward arg lines and then to the first nonblank character on that line. It returns
nil. If arg is omitted ornil, it defaults to 1.
This command moves point forward arg lines and then to the first nonblank character on that line. It returns
nil. If arg is omitted ornil, it defaults to 1.
The case change commands described here work on text in the current buffer. See Case Conversion, for case conversion functions that work on strings and characters. See Case Tables, for how to customize which characters are upper or lower case and how to convert them.
This function capitalizes all words in the region defined by start and end. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. The function returns
nil.If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word.
When
capitalize-regionis called interactively, start and end are point and the mark, with the smallest first.---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 44) ⇒ nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ----------
This function converts all of the letters in the region defined by start and end to lower case. The function returns
nil.When
downcase-regionis called interactively, start and end are point and the mark, with the smallest first.
This function converts all of the letters in the region defined by start and end to upper case. The function returns
nil.When
upcase-regionis called interactively, start and end are point and the mark, with the smallest first.
This function capitalizes count words after point, moving point over as it does. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. If count is negative, the function capitalizes the −count previous words but does not move point. The value is
nil.If point is in the middle of a word, the part of the word before point is ignored when moving forward. The rest is treated as an entire word.
When
capitalize-wordis called interactively, count is set to the numeric prefix argument.
This function converts the count words after point to all lower case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is
nil.When
downcase-wordis called interactively, count is set to the numeric prefix argument.
This function converts the count words after point to all upper case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is
nil.When
upcase-wordis called interactively, count is set to the numeric prefix argument.
Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see Property Lists). The properties belong to a particular character at a particular place, such as, the letter ‘T’ at the beginning of this sentence or the first ‘o’ in ‘foo’—if the same character occurs in two different places, the two occurrences in general have different properties.
Each property has a name and a value. Both of these can be any Lisp
object, but the name is normally a symbol. Typically each property
name symbol is used for a particular purpose; for instance, the text
property face specifies the faces for displaying the character
(see Special Properties). The usual way to access the property
list is to specify a name and ask what value corresponds to it.
If a character has a category property, we call it the
property category of the character. It should be a symbol. The
properties of the symbol serve as defaults for the properties of the
character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
substring, insert, and buffer-substring.
The simplest way to examine text properties is to ask for the value of
a particular property of a particular character. For that, use
get-text-property. Use text-properties-at to get the
entire property list of a character. See Property Search, for
functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1.
This function returns the value of the prop property of the character after position pos in object (a buffer or string). The argument object is optional and defaults to the current buffer.
If there is no prop property strictly speaking, but the character has a property category that is a symbol, then
get-text-propertyreturns the prop property of that symbol.
This function is like
get-text-property, except that it checks overlays first and then text properties. See Overlays.The argument object may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If object is a buffer, then overlays in that buffer are considered first, in order of decreasing priority, followed by the text properties. If object is a string, only text properties are considered, since strings never have overlays.
This is like
get-char-property, but gives extra information about the overlay that the property value comes from.Its value is a cons cell whose car is the property value, the same value
get-char-propertywould return with the same arguments. Its cdr is the overlay in which the property was found, ornil, if it was found as a text property or not found at all.If position is at the end of object, both the car and the cdr of the value are
nil.
This variable holds an alist which maps property names to a list of alternative property names. If a character does not specify a direct value for a property, the alternative property names are consulted in order; the first non-
nilvalue is used. This variable takes precedence overdefault-text-properties, andcategoryproperties take precedence over this variable.
This function returns the entire property list of the character at position in the string or buffer object. If object is
nil, it defaults to the current buffer.
This variable holds a property list giving default values for text properties. Whenever a character does not specify a value for a property, neither directly, through a category symbol, or through
char-property-alias-alist, the value stored in this list is used instead. Here is an example:(setq default-text-properties '(foo 69) char-property-alias-alist nil) ;; Make sure character 1 has no properties of its own. (set-text-properties 1 2 nil) ;; What we get, when we ask, is the default value. (get-text-property 1 'foo) ⇒ 69
The primitives for changing properties apply to a specified range of
text in a buffer or string. The function set-text-properties
(see end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.
Since text properties are considered part of the contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties marks the buffer as modified. Buffer text property changes are undoable also (see Undo). Positions in a string start from 0, whereas positions in a buffer start from 1.
This function sets the prop property to value for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.
This function adds or overrides text properties for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props specifies which properties to add. It should have the form of a property list (see Property Lists): a list whose elements include the property names followed alternately by the corresponding values.
The return value is
tif the function actually changed some property's value;nilotherwise (if props isnilor its values agree with those in the text).For example, here is how to set the
commentandfaceproperties of a range of text:(add-text-properties start end '(comment t face highlight))
This function deletes specified text properties from the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props specifies which properties to delete. It should have the form of a property list (see Property Lists): a list whose elements are property names alternating with corresponding values. But only the names matter—the values that accompany them are ignored. For example, here's how to remove the
faceproperty.(remove-text-properties start end '(face nil))The return value is
tif the function actually changed some property's value;nilotherwise (if props isnilor if no character in the specified text had any of those properties).To remove all text properties from certain text, use
set-text-propertiesand specifynilfor the new property list.
Like
remove-text-propertiesexcept that list-of-properties is a list of property names only, not an alternating list of property names and values.
This function completely replaces the text property list for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values.
After
set-text-propertiesreturns, all the characters in the specified range have identical properties.If props is
nil, the effect is to get rid of all properties from the specified range of text. Here's an example:(set-text-properties start end nil)Do not rely on the return value of this function.
The easiest way to make a string with text properties
is with propertize:
This function returns a copy of string which has the text properties properties. These properties apply to all the characters in the string that is returned. Here is an example that constructs a string with a
faceproperty and amouse-faceproperty:(propertize "foo" 'face 'italic 'mouse-face 'bold-italic) ⇒ #("foo" 0 3 (mouse-face bold-italic face italic))To put different properties on various parts of a string, you can construct each part with
propertizeand then combine them withconcat:(concat (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) " and " (propertize "bar" 'face 'italic 'mouse-face 'bold-italic)) ⇒ #("foo and bar" 0 3 (face italic mouse-face bold-italic) 3 8 nil 8 11 (face italic mouse-face bold-italic))
See also the function buffer-substring-no-properties
(see Buffer Contents) which copies text from the buffer
but does not copy its properties.
In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use eq for
comparing property values. In all cases, object defaults to the
current buffer.
For high performance, it's very important to use the limit argument to these functions, especially the ones that search for a single property—otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position (or
nil). Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.
The function scans the text forward from position pos in the string or buffer object till it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose properties are not identical to those of the character just after pos.
If limit is non-
nil, then the scan ends at position limit. If there is no property change before that point,next-property-changereturns limit.The value is
nilif the properties remain unchanged all the way to the end of object and limit isnil. If the value is non-nil, it is a position greater than or equal to pos. The value equals pos only when limit equals pos.Here is an example of how to scan the buffer by chunks of text within which all properties are constant:
(while (not (eobp)) (let ((plist (text-properties-at (point))) (next-change (or (next-property-change (point) (current-buffer)) (point-max)))) Process text from point to next-change... (goto-char next-change)))
This is like
next-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.
The function scans text for a change in the prop property, then returns the position of the change. The scan goes forward from position pos in the string or buffer object. In other words, this function returns the position of the first character beyond pos whose prop property differs from that of the character just after pos.
If limit is non-
nil, then the scan ends at position limit. If there is no property change before that point,next-single-property-changereturns limit.The value is
nilif the property remains unchanged all the way to the end of object and limit isnil. If the value is non-nil, it is a position greater than or equal to pos; it equals pos only if limit equals pos.
This is like
next-single-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.
This is like
next-property-changeexcept that it considers overlay properties as well as text properties, and if no change is found before the end of the buffer, it returns the maximum buffer position rather thannil(in this sense, it resembles the corresponding overlay functionnext-overlay-change, rather thannext-property-change). There is no object operand because this function operates only on the current buffer. It returns the next address at which either kind of property changes.
This is like
next-char-property-change, but scans back from pos instead of forward, and returns the minimum buffer position if no change is found.
This is like
next-single-property-changeexcept that it considers overlay properties as well as text properties, and if no change is found before the end of the object, it returns the maximum valid position in object rather thannil. Unlikenext-char-property-change, this function does have an object operand; if object is not a buffer, only text-properties are considered.
This is like
next-single-char-property-change, but scans back from pos instead of forward, and returns the minimum valid position in object if no change is found.
This function returns non-
nilif at least one character between start and end has a property prop whose value is value. More precisely, it returns the position of the first such character. Otherwise, it returnsnil.The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
This function returns non-
nilif at least one character between start and end does not have a property prop with value value. More precisely, it returns the position of the first such character. Otherwise, it returnsnil.The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like.
Note: the properties composition, display,
invisible and intangible can also cause point to move to
an acceptable place, after each Emacs command. See Adjusting Point.
categorycategory property, we call it the
property category of the character. It should be a symbol. The
properties of this symbol serve as defaults for the properties of the
character.
faceface to control the font and color of
text. See Faces, for more information.
In the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities;
(foreground-color . color-name)
or (background-color . color-name). These are old,
deprecated equivalents for (:foreground color-name) and
(:background color-name). Please convert code that uses
them.
It works to use the latter two forms directly as the value
of the face property.
Font Lock mode (see Font Lock Mode) works in most buffers by
dynamically updating the face property of characters based on
the context.
font-lock-facefont-lock-face property is equivalent to the face
property when Font Lock mode is enabled. When Font Lock mode is disabled,
font-lock-face has no effect.
The font-lock-face property is useful for special modes that
implement their own highlighting. See Precalculated Fontification.
mouse-facemouse-face is used instead of face when the
mouse is on or near the character. For this purpose, “near” means
that all text between the character and where the mouse is have the same
mouse-face property value.
fontifiednil, Emacs's redisplay routine calls the functions in
fontification-functions (see Auto Faces) to prepare this
part of the buffer before it is displayed. It is used internally by
the “just in time” font locking code.
displayhelp-echohelp-echo property, then when you
move the mouse onto that text, Emacs displays that string in the echo
area, or in the tooltip window (see Tooltips).
If the value of the help-echo property is a function, that
function is called with three arguments, window, object and
pos and should return a help string or nil for
none. The first argument, window is the window in which
the help was found. The second, object, is the buffer, overlay or
string which had the help-echo property. The pos
argument is as follows:
help-echo
property, and pos is the position in the overlay's buffer.
display property), pos is the position in that
string.
If the value of the help-echo property is neither a function nor
a string, it is evaluated to obtain a help string.
You can alter the way help text is displayed by setting the variable
show-help-function (see Help display).
This feature is used in the mode line and for other active text.
keymapkeymap property specifies an additional keymap for
commands. When this keymap applies, it is used for key lookup before
the minor mode keymaps and before the buffer's local map.
See Active Keymaps. If the property value is a symbol, the
symbol's function definition is used as the keymap.
The property's value for the character before point applies if it is
non-nil and rear-sticky, and the property's value for the
character after point applies if it is non-nil and
front-sticky. (For mouse clicks, the position of the click is used
instead of the position of point.)
local-mapkeymap except that it specifies a
keymap to use instead of the buffer's local map. For most
purposes (perhaps all purposes), it is better to use the keymap
property.
syntax-tablesyntax-table property overrides what the syntax table says
about this particular character. See Syntax Properties.
read-onlyread-only, then modifying that
character is not allowed. Any command that would do so gets an error,
text-read-only. If the property value is a string, that string
is used as the error message.
Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the read-only property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. See Sticky Properties.
Since changing properties counts as modifying the buffer, it is not
possible to remove a read-only property unless you know the
special trick: bind inhibit-read-only to a non-nil value
and then remove the property. See Read Only Buffers.
invisiblenil invisible property can make a character invisible
on the screen. See Invisible Text, for details.
intangiblenil
intangible properties, then you cannot place point between them.
If you try to move point forward into the group, point actually moves to
the end of the group. If you try to move point backward into the group,
point actually moves to the start of the group.
If consecutive characters have unequal non-nil
intangible properties, they belong to separate groups; each
group is separately treated as described above.
When the variable inhibit-point-motion-hooks is non-nil,
the intangible property is ignored.
fieldfield property constitute a
field. Some motion functions including forward-word and
beginning-of-line stop moving at a field boundary.
See Fields.
cursornil cursor text property. In
addition, if the value of the cursor property of an overlay
string is an integer number, it specifies the number of buffer's
character positions associated with the overlay string; this way,
Emacs will display the cursor on the character with that property
regardless of whether the current buffer position is actually covered
by the overlay. Specifically, if the value of the cursor
property of a character is the number n, the cursor will be
displayed on this character for any buffer position in the range
[ovpos..ovpos+n], where ovpos is the
starting buffer position covered by the overlay (see Managing Overlays).
pointerline-spacingline-spacing text or overlay property that
controls the height of the display line ending with that newline. The
property value overrides the default frame line spacing and the buffer
local line-spacing variable. See Line Height.
line-heightline-height text or overlay property that
controls the total height of the display line ending in that newline.
See Line Height.
wrap-prefixwrap-prefix property, the prefix it defines will
be added at display-time to the beginning of every continuation line
due to text wrapping (so if lines are truncated, the wrap-prefix is
never used). It may be a string, an image, or a stretch-glyph such as
used by the display text-property. See Display Property.
A wrap-prefix may also be specified for an entire buffer using the
wrap-prefix buffer-local variable (however, a
wrap-prefix text-property takes precedence over the value of
the wrap-prefix variable). See Truncation.
line-prefixline-prefix property, the prefix it defines will
be added at display-time to the beginning of every non-continuation
line. It may be a string, an image, or a stretch-glyph such as used
by the display text-property. See Display Property.
A line-prefix may also be specified for an entire buffer using the
line-prefix buffer-local variable (however, a
line-prefix text-property takes precedence over the value of
the line-prefix variable). See Truncation.
modification-hooksmodification-hooks, then its
value should be a list of functions; modifying that character calls all
of those functions. Each function receives two arguments: the beginning
and end of the part of the buffer being modified. Note that if a
particular modification hook function appears on several characters
being modified by a single primitive, you can't predict how many times
the function will be called.
If these functions modify the buffer, they should bind
inhibit-modification-hooks to t around doing so, to
avoid confusing the internal mechanism that calls these hooks.
Overlays also support the modification-hooks property, but the
details are somewhat different (see Overlay Properties).
insert-in-front-hooksinsert-behind-hooksinsert-in-front-hooks property of the following
character and in the insert-behind-hooks property of the
preceding character. These functions receive two arguments, the
beginning and end of the inserted text. The functions are called
after the actual insertion takes place.
See also Change Hooks, for other hooks that are called
when you change text in a buffer.
point-enteredpoint-leftpoint-entered and point-left
record hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
point-left property of the character after the old location,
and
point-entered property of the character after the new
location.
If these two values differ, each of them is called (if not nil)
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and new
locations. The result may be to execute two point-left functions
(which may be the same function) and/or two point-entered
functions (which may be the same function). In any case, all the
point-left functions are called first, followed by all the
point-entered functions.
It is possible with char-after to examine characters at various
buffer positions without moving point to those positions. Only an
actual change in the value of point runs these hook functions.
When this variable is non-
nil,point-leftandpoint-enteredhooks are not run, and theintangibleproperty has no effect. Do not set this variable globally; bind it withlet.
If this variable is non-
nil, it specifies a function called to display help strings. These may behelp-echoproperties, menu help strings (see Simple Menu Items, see Extended Menu Items), or tool bar help strings (see Tool Bar). The specified function is called with one argument, the help string to display. Tooltip mode (see Tooltips) provides an example.
compositionput-text-property.
These text properties affect the behavior of the fill commands. They are used for representing formatted text. See Filling, and Margins.
harduse-hard-newlines minor mode is enabled. See Hard and Soft Newlines.
right-marginleft-marginjustificationSelf-inserting characters normally take on the same properties as the preceding character. This is called inheritance of properties.
In a Lisp program, you can do insertion with inheritance or without,
depending on your choice of insertion primitive. The ordinary text
insertion functions such as insert do not inherit any properties.
They insert text with precisely the properties of the string being
inserted, and no others. This is correct for programs that copy text
from one context to another—for example, into or out of the kill ring.
To insert with inheritance, use the special primitives described in this
section. Self-inserting characters inherit properties because they work
using these primitives.
When you do insertion with inheritance, which properties are inherited, and from where, depends on which properties are sticky. Insertion after a character inherits those of its properties that are rear-sticky. Insertion before a character inherits those of its properties that are front-sticky. When both sides offer different sticky values for the same property, the previous character's value takes precedence.
By default, a text property is rear-sticky but not front-sticky; thus, the default is to inherit all the properties of the preceding character, and nothing from the following character.
You can control the stickiness of various text properties with two
specific text properties, front-sticky and rear-nonsticky,
and with the variable text-property-default-nonsticky. You can
use the variable to specify a different default for a given property.
You can use those two text properties to make any specific properties
sticky or nonsticky in any particular part of the text.
If a character's front-sticky property is t, then all
its properties are front-sticky. If the front-sticky property is
a list, then the sticky properties of the character are those whose
names are in the list. For example, if a character has a
front-sticky property whose value is (face read-only),
then insertion before the character can inherit its face property
and its read-only property, but no others.
The rear-nonsticky property works the opposite way. Most
properties are rear-sticky by default, so the rear-nonsticky
property says which properties are not rear-sticky. If a
character's rear-nonsticky property is t, then none of its
properties are rear-sticky. If the rear-nonsticky property is a
list, properties are rear-sticky unless their names are in the
list.
This variable holds an alist which defines the default rear-stickiness of various text properties. Each element has the form
(property.nonstickiness), and it defines the stickiness of a particular text property, property.If nonstickiness is non-
nil, this means that the property property is rear-nonsticky by default. Since all properties are front-nonsticky by default, this makes property nonsticky in both directions by default.The text properties
front-stickyandrear-nonsticky, when used, take precedence over the default nonstickiness specified intext-property-default-nonsticky.
Here are the functions that insert text with inheritance of properties:
Insert the strings strings, just like the function
insert, but inherit any sticky properties from the adjoining text.
Insert the strings strings, just like the function
insert-before-markers, but inherit any sticky properties from the adjoining text.
See Insertion, for the ordinary insertion functions which do not inherit.
Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them.
The primitive that extracts text from the buffer along with its
properties is buffer-substring. Before examining the properties,
this function runs the abnormal hook buffer-access-fontify-functions.
This variable holds a list of functions for computing text properties. Before
buffer-substringcopies the text and text properties for a portion of the buffer, it calls all the functions in this list. Each of the functions receives two arguments that specify the range of the buffer being accessed. (The buffer itself is always the current buffer.)
The function buffer-substring-no-properties does not call these
functions, since it ignores text properties anyway.
In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
buffer-access-fontified-property.
If this variable's value is non-
nil, it is a symbol which is used as a text property name. A non-nilvalue for that text property means, “the other text properties for this character have already been computed.”If all the characters in the range specified for
buffer-substringhave a non-nilvalue for this property,buffer-substringdoes not call thebuffer-access-fontify-functionsfunctions. It assumes these characters already have the right text properties, and just copies the properties they already have.The normal way to use this feature is that the
buffer-access-fontify-functionsfunctions add this property, as well as others, to the characters they operate on. That way, they avoid being called over and over for the same text.
Clickable text is text that can be clicked, with either the mouse or via a keyboard command, to produce some result. Many major modes use clickable text to implement textual hyper-links, or links for short.
The easiest way to insert and manipulate links is to use the
button package. See Buttons. In this section, we will
explain how to manually set up clickable text in a buffer, using text
properties. For simplicity, we will refer to the clickable text as a
link.
Implementing a link involves three separate steps: (1) indicating
clickability when the mouse moves over the link; (2) making RET
or Mouse-2 on that link do something; and (3) setting up a
follow-link condition so that the link obeys
mouse-1-click-follows-link.
To indicate clickability, add the mouse-face text property to
the text of the link; then Emacs will highlight the link when the
mouse moves over it. In addition, you should define a tooltip or echo
area message, using the help-echo text property. See Special Properties. For instance, here is how Dired indicates that file
names are clickable:
(if (dired-move-to-filename)
(add-text-properties
(point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'(mouse-face highlight
help-echo "mouse-2: visit this file in other window")))
To make the link clickable, bind <RET> and Mouse-2 to commands that perform the desired action. Each command should check to see whether it was called on a link, and act accordingly. For instance, Dired's major mode keymap binds Mouse-2 to the following command:
(defun dired-mouse-find-file-other-window (event)
"In Dired, visit the file or directory name you click on."
(interactive "e")
(let ((window (posn-window (event-end event)))
(pos (posn-point (event-end event)))
file)
(if (not (windowp window))
(error "No file chosen"))
(with-current-buffer (window-buffer window)
(goto-char pos)
(setq file (dired-get-file-for-visit)))
(if (file-directory-p file)
(or (and (cdr dired-subdir-alist)
(dired-goto-subdir file))
(progn
(select-window window)
(dired-other-window file)))
(select-window window)
(find-file-other-window (file-name-sans-versions file t)))))
This command uses the functions posn-window and
posn-point to determine where the click occurred, and
dired-get-file-for-visit to determine which file to visit.
Instead of binding the mouse command in a major mode keymap, you can
bind it within the link text, using the keymap text property
(see Special Properties). For instance:
(let ((map (make-sparse-keymap)))
(define-key map [mouse-2] 'operate-this-button)
(put-text-property link-start link-end 'keymap map))
With this method, you can easily define different commands for different links. Furthermore, the global definition of <RET> and Mouse-2 remain available for the rest of the text in the buffer.
The basic Emacs command for clicking on links is Mouse-2.
However, for compatibility with other graphical applications, Emacs
also recognizes Mouse-1 clicks on links, provided the user
clicks on the link quickly without moving the mouse. This behavior is
controlled by the user option mouse-1-click-follows-link.
See Mouse References.
To set up the link so that it obeys
mouse-1-click-follows-link, you must either (1) apply a
follow-link text or overlay property to the link text, or (2)
bind the follow-link event to a keymap (which can be a major
mode keymap or a local keymap specified via the keymap text
property). The value of the follow-link property, or the
binding for the follow-link event, acts as a “condition” for
the link action. This condition tells Emacs two things: the
circumstances under which a Mouse-1 click should be regarded as
occurring “inside” the link, and how to compute an “action code”
that says what to translate the Mouse-1 click into. The link
action condition can be one of the following:
mouse-facemouse-face, a position is inside
a link if there is a non-nil mouse-face property at that
position. The action code is always t.
For example, here is how Info mode handles <Mouse-1>:
(define-key Info-mode-map [follow-link] 'mouse-face)
(func pos) evaluates to
non-nil. The value returned by func serves as the action
code.
For example, here is how pcvs enables Mouse-1 to follow links on file names only:
(define-key map [follow-link]
(lambda (pos)
(eq (get-char-property pos 'face) 'cvs-filename-face)))
The action code tells Mouse-1 how to follow the link:
"foo",
Mouse-1 translates into f. If it is [foo],
Mouse-1 translates into <foo>.
nil action code, the Mouse-1 event is
translated into a Mouse-2 event at the same position.
To define Mouse-1 to activate a button defined with
define-button-type, give the button a follow-link
property. The property value should be a link action condition, as
described above. See Buttons. For example, here is how Help mode
handles Mouse-1:
(define-button-type 'help-xref
'follow-link t
'action #'help-button-action)
To define Mouse-1 on a widget defined with
define-widget, give the widget a :follow-link property.
The property value should be a link action condition, as described
above. For example, here is how the link widget specifies that
a <Mouse-1> click shall be translated to <RET>:
(define-widget 'link 'item
"An embedded link."
:button-prefix 'widget-link-prefix
:button-suffix 'widget-link-suffix
:follow-link "\C-m"
:help-echo "Follow the link."
:format "%[%t%]")
This function returns non-
nilif position pos in the current buffer is on a link. pos can also be a mouse event location, as returned byevent-start(see Accessing Mouse).
A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with eq) of the
field property (either a text-property or an overlay property).
This section describes special functions that are available for
operating on fields.
You specify a field with a buffer position, pos. We think of each field as containing a range of buffer positions, so the position you specify stands for the field containing that position.
When the characters before and after pos are part of the same
field, there is no doubt which field contains pos: the one those
characters both belong to. When pos is at a boundary between
fields, which field it belongs to depends on the stickiness of the
field properties of the two surrounding characters (see Sticky Properties). The field whose property would be inherited by text
inserted at pos is the field that contains pos.
There is an anomalous case where newly inserted text at pos
would not inherit the field property from either side. This
happens if the previous character's field property is not
rear-sticky, and the following character's field property is not
front-sticky. In this case, pos belongs to neither the preceding
field nor the following field; the field functions treat it as belonging
to an empty field whose beginning and end are both at pos.
In all of these functions, if pos is omitted or nil, the
value of point is used by default. If narrowing is in effect, then
pos should fall within the accessible portion. See Narrowing.
This function returns the beginning of the field specified by pos.
If pos is at the beginning of its field, and escape-from-edge is non-
nil, then the return value is always the beginning of the preceding field that ends at pos, regardless of the stickiness of thefieldproperties around pos.If limit is non-
nil, it is a buffer position; if the beginning of the field is before limit, then limit will be returned instead.
This function returns the end of the field specified by pos.
If pos is at the end of its field, and escape-from-edge is non-
nil, then the return value is always the end of the following field that begins at pos, regardless of the stickiness of thefieldproperties around pos.If limit is non-
nil, it is a buffer position; if the end of the field is after limit, then limit will be returned instead.
This function returns the contents of the field specified by pos, as a string.
This function returns the contents of the field specified by pos, as a string, discarding text properties.
This function deletes the text of the field specified by pos.
This function “constrains” new-pos to the field that old-pos belongs to—in other words, it returns the position closest to new-pos that is in the same field as old-pos.
If new-pos is
nil, thenconstrain-to-fielduses the value of point instead, and moves point to the resulting position as well as returning it.If old-pos is at the boundary of two fields, then the acceptable final positions depend on the argument escape-from-edge. If escape-from-edge is
nil, then new-pos must be in the field whosefieldproperty equals what new characters inserted at old-pos would inherit. (This depends on the stickiness of thefieldproperty for the characters before and after old-pos.) If escape-from-edge is non-nil, new-pos can be anywhere in the two adjacent fields. Additionally, if two fields are separated by another field with the special valueboundary, then any point within this special field is also considered to be “on the boundary.”Commands like C-a with no argumemt, that normally move backward to a specific kind of location and stay there once there, probably should specify
nilfor escape-from-edge. Other motion commands that check fields should probably passt.If the optional argument only-in-line is non-
nil, and constraining new-pos in the usual way would move it to a different line, new-pos is returned unconstrained. This used in commands that move by line, such asnext-lineandbeginning-of-line, so that they respect field boundaries only in the case where they can still move to the right line.If the optional argument inhibit-capture-property is non-
nil, and old-pos has a non-nilproperty of that name, then any field boundaries are ignored.You can cause
constrain-to-fieldto ignore all field boundaries (and so never constrain anything) by binding the variableinhibit-field-text-motionto a non-nilvalue.
Some editors that support adding attributes to text in the buffer do so by letting the user specify “intervals” within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two.
Suppose we “fix” this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. One again, editing does not preserve the distinction between one interval and two.
Insertion of text at the border between intervals also raises questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for questions of the form, “What are the properties of this character?” So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end.
In practice, you can usually use the text property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See Property Search.
Emacs also provides explicit intervals as a presentation feature; see Overlays.
The following functions replace characters within a specified region based on their character codes.
This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.
If noundo is non-
nil, thensubst-char-in-regiondoes not record the change for undo and does not mark the buffer as modified. This was useful for controlling the old selective display feature (see Selective Display).
subst-char-in-regiondoes not move point and returnsnil.---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- (subst-char-in-region 1 20 ?i ?X) ⇒ nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ----------
This function applies a translation table to the characters in the buffer between positions start and end.
The translation table table is a string or a char-table;
(areftable ochar)gives the translated character corresponding to ochar. If table is a string, any characters with codes larger than the length of table are not altered by the translation.The return value of
translate-regionis the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table.
A register is a sort of variable used in Emacs editing that can hold a variety of different kinds of values. Each register is named by a single character. All ASCII characters and their meta variants (but with the exception of C-g) can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by the character that is its name.
This variable is an alist of elements of the form
(name.contents). Normally, there is one element for each Emacs register that has been used.The object name is a character (an integer) identifying the register.
The contents of a register can have several possible types:
insert-register finds a number
in the register, it converts the number to decimal.
(window-configuration position)(frame-configuration position)The functions in this section return unpredictable values unless otherwise stated.
This function returns the contents of the register reg, or
nilif it has no contents.
This function sets the contents of register reg to value. A register can be set to any value, but the other register functions expect only certain data types. The return value is value.
This command inserts contents of register reg into the current buffer.
Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument beforep is non-
nil, it puts the mark before and point after. You can pass a non-nilsecond argument beforep to this function interactively by supplying any prefix argument.If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines.
If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future.
This subroutine is used by the transposition commands.
This function exchanges two nonoverlapping portions of the buffer. Arguments start1 and end1 specify the bounds of one portion and arguments start2 and end2 specify the bounds of the other portion.
Normally,
transpose-regionsrelocates markers with the transposed text; a marker previously positioned within one of the two transposed portions moves along with that portion, thus remaining between the same two characters in their new position. However, if leave-markers is non-nil,transpose-regionsdoes not do this—it leaves all markers unrelocated.
Base 64 code is used in email to encode a sequence of 8-bit bytes as a longer sequence of ASCII graphic characters. It is defined in Internet RFC122045. This section describes the functions for converting to and from this code.
This function converts the region from beg to end into base 64 code. It returns the length of the encoded text. An error is signaled if a character in the region is multibyte, i.e. in a multibyte buffer the region must contain only characters from the charsets
ascii,eight-bit-controlandeight-bit-graphic.Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument no-line-break is non-
nil, these newlines are not added, so the output is just one long line.
This function converts the string string into base 64 code. It returns a string containing the encoded text. As for
base64-encode-region, an error is signaled if a character in the string is multibyte.Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument no-line-break is non-
nil, these newlines are not added, so the result string is just one long line.
This function converts the region from beg to end from base 64 code into the corresponding decoded text. It returns the length of the decoded text.
The decoding functions ignore newline characters in the encoded text.
This function converts the string string from base 64 code into the corresponding decoded text. It returns a unibyte string containing the decoded text.
The decoding functions ignore newline characters in the encoded text.
MD5 cryptographic checksums, or message digests, are 128-bit “fingerprints” of a document or program. They are used to verify that you have an exact and unaltered copy of the data. The algorithm to calculate the MD5 message digest is defined in Internet RFC131321. This section describes the Emacs facilities for computing message digests.
This function returns the MD5 message digest of object, which should be a buffer or a string.
The two optional arguments start and end are character positions specifying the portion of object to compute the message digest for. If they are
nilor omitted, the digest is computed for the whole of object.The function
md5does not compute the message digest directly from the internal Emacs representation of the text (see Text Representations). Instead, it encodes the text using a coding system, and computes the message digest from the encoded text. The optional fourth argument coding-system specifies which coding system to use for encoding the text. It should be the same coding system that you used to read the text, or that you used or will use when saving or sending the text. See Coding Systems, for more information about coding systems.If coding-system is
nilor omitted, the default depends on object. If object is a buffer, the default for coding-system is whatever coding system would be chosen by default for writing this text into a file. If object is a string, the user's most preferred coding system (see prefer-coding-system) is used.Normally,
md5signals an error if the text can't be encoded using the specified or chosen coding system. However, if noerror is non-nil, it silently usesraw-textcoding instead.
In data base terminology, an atomic change is an indivisible change—it can succeed entirely or it can fail entirely, but it cannot partly succeed. A Lisp program can make a series of changes to one or several buffers as an atomic change group, meaning that either the entire series of changes will be installed in their buffers or, in case of an error, none of them will be.
To do this for one buffer, the one already current, simply write a
call to atomic-change-group around the code that makes the
changes, like this:
(atomic-change-group
(insert foo)
(delete-region x y))
If an error (or other nonlocal exit) occurs inside the body of
atomic-change-group, it unmakes all the changes in that buffer
that were during the execution of the body. This kind of change group
has no effect on any other buffers—any such changes remain.
If you need something more sophisticated, such as to make changes in
various buffers constitute one atomic group, you must directly call
lower-level functions that atomic-change-group uses.
This function sets up a change group for buffer buffer, which defaults to the current buffer. It returns a “handle” that represents the change group. You must use this handle to activate the change group and subsequently to finish it.
To use the change group, you must activate it. You must do this before making any changes in the text of buffer.
This function activates the change group that handle designates.
After you activate the change group, any changes you make in that buffer become part of it. Once you have made all the desired changes in the buffer, you must finish the change group. There are two ways to do this: you can either accept (and finalize) all the changes, or cancel them all.
This function accepts all the changes in the change group specified by handle, making them final.
This function cancels and undoes all the changes in the change group specified by handle.
Your code should use unwind-protect to make sure the group is
always finished. The call to activate-change-group should be
inside the unwind-protect, in case the user types C-g
just after it runs. (This is one reason why
prepare-change-group and activate-change-group are
separate functions, because normally you would call
prepare-change-group before the start of that
unwind-protect.) Once you finish the group, don't use the
handle again—in particular, don't try to finish the same group
twice.
To make a multibuffer change group, call prepare-change-group
once for each buffer you want to cover, then use nconc to
combine the returned values, like this:
(nconc (prepare-change-group buffer-1)
(prepare-change-group buffer-2))
You can then activate the multibuffer change group with a single call
to activate-change-group, and finish it with a single call to
accept-change-group or cancel-change-group.
Nested use of several change groups for the same buffer works as you would expect. Non-nested use of change groups for the same buffer will get Emacs confused, so don't let it happen; the first change group you start for any given buffer should be the last one finished.
These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also Special Properties, for how to detect changes to specific parts of the text.
The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them.
This variable holds a list of functions to call before any buffer modification. Each function gets two arguments, the beginning and end of the region that is about to change, represented as integers. The buffer that is about to change is always the current buffer.
This variable holds a list of functions to call after any buffer modification. Each function receives three arguments: the beginning and end of the region just changed, and the length of the text that existed before the change. All three arguments are integers. The buffer that's about to change is always the current buffer.
The length of the old text is the difference between the buffer positions before and after that text as it was before the change. As for the changed text, its length is simply the difference between the first two arguments.
Output of messages into the ‘*Messages*’ buffer does not call these functions.
The macro executes body normally, but arranges to call the after-change functions just once for a series of several changes—if that seems safe.
If a program makes several text changes in the same area of the buffer, using the macro
combine-after-change-callsaround that part of the program can make it run considerably faster when after-change hooks are in use. When the after-change hooks are ultimately called, the arguments specify a portion of the buffer including all of the changes made within thecombine-after-change-callsbody.Warning: You must not alter the values of
after-change-functionswithin the body of acombine-after-change-callsform.Warning: if the changes you combine occur in widely scattered parts of the buffer, this will still work, but it is not advisable, because it may lead to inefficient behavior for some change hook functions.
This variable is a normal hook that is run whenever a buffer is changed that was previously in the unmodified state.
If this variable is non-
nil, all of the change hooks are disabled; none of them run. This affects all the hook variables described above in this section, as well as the hooks attached to certain special text properties (see Special Properties) and overlay properties (see Overlay Properties).Also, this variable is bound to non-
nilwhile running those same hook variables, so that by default modifying the buffer from a modification hook does not cause other modification hooks to be run. If you do want modification hooks to be run in a particular piece of code that is itself run from a modification hook, then rebind locallyinhibit-modification-hookstonil.
This chapter covers the special issues relating to characters and how they are stored in strings and buffers.
Emacs buffers and strings support a large repertoire of characters from many different scripts, allowing users to type and display text in almost any known written language.
To support this multitude of characters and scripts, Emacs closely
follows the Unicode Standard. The Unicode Standard assigns a
unique number, called a codepoint, to each and every character.
The range of codepoints defined by Unicode, or the Unicode
codespace, is 0..#x10FFFF (in hexadecimal notation),
inclusive. Emacs extends this range with codepoints in the range
#x110000..#x3FFFFF, which it uses for representing characters
that are not unified with Unicode and raw 8-bit bytes that
cannot be interpreted as characters. Thus, a character codepoint in
Emacs is a 22-bit integer number.
To conserve memory, Emacs does not hold fixed-length 22-bit numbers that are codepoints of text characters within buffers and strings. Rather, Emacs uses a variable-length internal representation of characters, that stores each character as a sequence of 1 to 5 8-bit bytes, depending on the magnitude of its codepoint14. For example, any ASCII character takes up only 1 byte, a Latin-1 character takes up 2 bytes, etc. We call this representation of text multibyte.
Outside Emacs, characters can be represented in many different encodings, such as ISO-8859-1, GB-2312, Big-5, etc. Emacs converts between these external encodings and its internal representation, as appropriate, when it reads text into a buffer or a string, or when it writes text to a disk file or passes it to some other process.
Occasionally, Emacs needs to hold and manipulate encoded text or binary non-text data in its buffers or strings. For example, when Emacs visits a file, it first reads the file's text verbatim into a buffer, and only then converts it to the internal representation. Before the conversion, the buffer holds encoded text.
Encoded text is not really text, as far as Emacs is concerned, but
rather a sequence of raw 8-bit bytes. We call buffers and strings
that hold encoded text unibyte buffers and strings, because
Emacs treats them as a sequence of individual bytes. Usually, Emacs
displays unibyte buffers and strings as octal codes such as
\237. We recommend that you never use unibyte buffers and
strings except for manipulating encoded text or binary non-text data.
In a buffer, the buffer-local value of the variable
enable-multibyte-characters specifies the representation used.
The representation for a string is determined and recorded in the string
when the string is constructed.
This variable specifies the current buffer's text representation. If it is non-
nil, the buffer contains multibyte text; otherwise, it contains unibyte encoded text or binary non-text data.You cannot set this variable directly; instead, use the function
set-buffer-multibyteto change a buffer's representation.The ‘--unibyte’ command line option does its job by setting the default value to
nilearly in startup.
Buffer positions are measured in character units. This function returns the byte-position corresponding to buffer position position in the current buffer. This is 1 at the start of the buffer, and counts upward in bytes. If position is out of range, the value is
nil.
Return the buffer position, in character units, corresponding to given byte-position in the current buffer. If byte-position is out of range, the value is
nil. In a multibyte buffer, an arbitrary value of byte-position can be not at character boundary, but inside a multibyte sequence representing a single character; in this case, this function returns the buffer position of the character whose multibyte sequence includes byte-position. In other words, the value does not change for all byte positions that belong to the same character.
This function returns the number of bytes in string. If string is a multibyte string, this can be greater than
(lengthstring).
This function concatenates all its argument bytes and makes the result a unibyte string.
Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte, provided that the multibyte text contains only ASCII and 8-bit raw bytes. In general, these conversions happen when inserting text into a buffer, or when putting text from several strings together in one string. You can also explicitly convert a string's contents to either representation.
Emacs chooses the representation for a string based on the text from which it is constructed. The general rule is to convert unibyte text to multibyte text when combining it with other multibyte text, because the multibyte representation is more general and can hold whatever characters the unibyte text has.
When inserting text into a buffer, Emacs converts the text to the
buffer's representation, as specified by
enable-multibyte-characters in that buffer. In particular, when
you insert multibyte text into a unibyte buffer, Emacs converts the text
to unibyte, even though this conversion cannot in general preserve all
the characters that might be in the multibyte text. The other natural
alternative, to convert the buffer contents to multibyte, is not
acceptable because the buffer's representation is a choice made by the
user that cannot be overridden automatically.
Converting unibyte text to multibyte text leaves ASCII characters unchanged, and converts bytes with codes 128 through 159 to the multibyte representation of raw eight-bit bytes.
Converting multibyte text to unibyte converts all ASCII and eight-bit characters to their single-byte form, but loses information for non-ASCII characters by discarding all but the low 8 bits of each character's codepoint. Converting unibyte text to multibyte and back to unibyte reproduces the original unibyte text.
The next two functions either return the argument string, or a newly created string with no text properties.
This function returns a multibyte string containing the same sequence of characters as string. If string is a multibyte string, it is returned unchanged. The function assumes that string includes only ASCII characters and raw 8-bit bytes; the latter are converted to their multibyte representation corresponding to the codepoints
#x3FFF80through#x3FFFFF, inclusive (see codepoints).
This function returns a unibyte string containing the same sequence of characters as string. It signals an error if string contains a non-ASCII character. If string is a unibyte string, it is returned unchanged. Use this function for string arguments that contain only ASCII and eight-bit characters.
This function returns a unibyte string containing a single byte of character data, character. It signals a error if character is not an integer between 0 and 255.
This converts the multibyte character char to a unibyte character, and returns that character. If char is neither ASCII nor eight-bit, the function returns -1.
This convert the unibyte character char to a multibyte character, assuming char is either ASCII or raw 8-bit byte.
Sometimes it is useful to examine an existing buffer or string as multibyte when it was unibyte, or vice versa.
Set the representation type of the current buffer. If multibyte is non-
nil, the buffer becomes multibyte. If multibyte isnil, the buffer becomes unibyte.This function leaves the buffer contents unchanged when viewed as a sequence of bytes. As a consequence, it can change the contents viewed as characters; for instance, a sequence of three bytes which is treated as one character in multibyte representation will count as three characters in unibyte representation. Eight-bit characters representing raw bytes are an exception. They are represented by one byte in a unibyte buffer, but when the buffer is set to multibyte, they are converted to two-byte sequences, and vice versa.
This function sets
enable-multibyte-charactersto record which representation is in use. It also adjusts various data in the buffer (including overlays, text properties and markers) so that they cover the same text as they did before.You cannot use
set-buffer-multibyteon an indirect buffer, because indirect buffers always inherit the representation of the base buffer.
If string is already a unibyte string, this function returns string itself. Otherwise, it returns a new string with the same bytes as string, but treating each byte as a separate character (so that the value may have more characters than string); as an exception, each eight-bit character representing a raw byte is converted into a single byte. The newly-created string contains no text properties.
If string is a multibyte string, this function returns string itself. Otherwise, it returns a new string with the same bytes as string, but treating each multibyte sequence as one character. This means that the value may have fewer characters than string has. If a byte sequence in string is invalid as a multibyte representation of a single character, each byte in the sequence is treated as a raw 8-bit byte. The newly-created string contains no text properties.
The unibyte and multibyte text representations use different
character codes. The valid character codes for unibyte representation
range from 0 to #xFF (255)—the values that can fit in one
byte. The valid character codes for multibyte representation range
from 0 to #x3FFFFF. In this code space, values 0 through
#x7F (127) are for ASCII characters, and values
#x80 (128) through #x3FFF7F (4194175) are for
non-ASCII characters.
Emacs character codes are a superset of the Unicode standard.
Values 0 through #x10FFFF (1114111) correspond to Unicode
characters of the same codepoint; values #x110000 (1114112)
through #x3FFF7F (4194175) represent characters that are not
unified with Unicode; and values #x3FFF80 (4194176) through
#x3FFFFF (4194303) represent eight-bit raw bytes.
This returns
tif charcode is a valid character, andnilotherwise.(characterp 65) ⇒ t (characterp 4194303) ⇒ t (characterp 4194304) ⇒ nil
This function returns the largest value that a valid character codepoint can have.
(characterp (max-char)) ⇒ t (characterp (1+ (max-char))) ⇒ nil
This function returns the byte at character position pos in the current buffer. If the current buffer is unibyte, this is literally the byte at that position. If the buffer is multibyte, byte values of ASCII characters are the same as character codepoints, whereas eight-bit raw bytes are converted to their 8-bit codes. The function signals an error if the character at pos is non-ASCII.
The optional argument string means to get a byte value from that string instead of the current buffer.
A character property is a named attribute of a character that specifies how the character behaves and how it should be handled during text processing and display. Thus, character properties are an important part of specifying the character's semantics.
On the whole, Emacs follows the Unicode Standard in its implementation of character properties. In particular, Emacs supports the Unicode Character Property Model, and the Emacs character property database is derived from the Unicode Character Database (UCD). See the Character Properties chapter of the Unicode Standard, for a detailed description of Unicode character properties and their meaning. This section assumes you are already familiar with that chapter of the Unicode Standard, and want to apply that knowledge to Emacs Lisp programs.
In Emacs, each property has a name, which is a symbol, and a set of
possible values, whose types depend on the property; if a character
does not have a certain property, the value is nil. As a
general rule, the names of character properties in Emacs are produced
from the corresponding Unicode properties by downcasing them and
replacing each ‘_’ character with a dash ‘-’. For example,
Canonical_Combining_Class becomes
canonical-combining-class. However, sometimes we shorten the
names to make their use easier.
Here is the full list of value types for all the character properties that Emacs knows about:
nameName property. The
value is a string consisting of upper-case Latin letters A to Z,
digits, spaces, and hyphen ‘-’ characters.
general-categoryGeneral_Category
property. The value is a symbol whose name is a 2-letter abbreviation
of the character's classification.
canonical-combining-classCanonical_Combining_Class property.
The value is an integer number.
bidi-classBidi_Class property. The value is a
symbol whose name is the Unicode directional type of the
character.
decompositionDecomposition_Type and
Decomposition_Value properties. The value is a list, whose
first element may be a symbol representing a compatibility formatting
tag, such as small15; the other elements are characters that give the compatibility
decomposition sequence of this character.
decimal-digit-valueNumeric_Value property for
characters whose Numeric_Type is ‘Digit’. The value is an
integer number.
digitNumeric_Value property for
characters whose Numeric_Type is ‘Decimal’. The value is
an integer number. Examples of such characters include compatibility
subscript and superscript digits, for which the value is the
corresponding number.
numeric-valueNumeric_Value property for
characters whose Numeric_Type is ‘Numeric’. The value of
this property is an integer or a floating-point number. Examples of
characters that have this property include fractions, subscripts,
superscripts, Roman numerals, currency numerators, and encircled
numbers. For example, the value of this property for the character
U+2155 (vulgar fraction one fifth) is 0.2.
mirroredBidi_Mirrored property. The value
of this property is a symbol, either Y or N.
old-nameUnicode_1_Name property. The value
is a string.
iso-10646-commentISO_Comment property. The value is
a string.
uppercaseSimple_Uppercase_Mapping property.
The value of this property is a single character.
lowercaseSimple_Lowercase_Mapping property.
The value of this property is a single character.
titlecaseSimple_Titlecase_Mapping property.
Title case is a special form of a character used when the first
character of a word needs to be capitalized. The value of this
property is a single character.
This function returns the value of char's propname property.
(get-char-code-property ? 'general-category) ⇒ Zs (get-char-code-property ?1 'general-category) ⇒ Nd (get-char-code-property ?\u2084 'digit-value) ; subscript 4 ⇒ 4 (get-char-code-property ?\u2155 'numeric-value) ; one fifth ⇒ 1/5 (get-char-code-property ?\u2163 'numeric-value) ; Roman IV ⇒ \4
This function returns the description string of property prop's value, or
nilif value has no description.(char-code-property-description 'general-category 'Zs) ⇒ "Separator, Space" (char-code-property-description 'general-category 'Nd) ⇒ "Number, Decimal Digit" (char-code-property-description 'numeric-value '1/5) ⇒ nil
This function stores value as the value of the property propname for the character char.
The value of this variable is a char-table (see Char-Tables) that specifies, for each character, a symbol whose name is the script to which the character belongs, according to the Unicode Standard classification of the Unicode code space into script-specific blocks. This char-table has a single extra slot whose value is the list of all script symbols.
The value of this variable is a char-table that specifies the width of each character in columns that it will occupy on the screen.
The value of this variable is a char-table that specifies, for each character, whether it is printable or not. That is, if evaluating
(aref printable-chars char)results int, the character is printable, and if it results innil, it is not.
An Emacs character set, or charset, is a set of characters
in which each character is assigned a numeric code point. (The
Unicode Standard calls this a coded character set.) Each Emacs
charset has a name which is a symbol. A single character can belong
to any number of different character sets, but it will generally have
a different code point in each charset. Examples of character sets
include ascii, iso-8859-1, greek-iso8859-7, and
windows-1255. The code point assigned to a character in a
charset is usually different from its code point used in Emacs buffers
and strings.
Emacs defines several special character sets. The character set
unicode includes all the characters whose Emacs code points are
in the range 0..#x10FFFF. The character set emacs
includes all ASCII and non-ASCII characters.
Finally, the eight-bit charset includes the 8-bit raw bytes;
Emacs uses it to represent raw bytes encountered in text.
Returns
tif object is a symbol that names a character set,nilotherwise.
This functions returns a list of all defined character sets ordered by their priority. If highestp is non-
nil, the function returns a single character set of the highest priority.
This function makes charsets the highest priority character sets.
This function returns the name of the character set of highest priority that character belongs to. ASCII characters are an exception: for them, this function always returns
ascii.If restriction is non-
nil, it should be a list of charsets to search. Alternatively, it can be a coding system, in which case the returned charset must be supported by that coding system (see Coding Systems).
This function returns the property list of the character set charset. Although charset is a symbol, this is not the same as the property list of that symbol. Charset properties include important information about the charset, such as its documentation string, short name, etc.
This function sets the propname property of charset to the given value.
This function returns the value of charsets property propname.
This command displays a list of characters in the character set charset.
Emacs can convert between its internal representation of a character and the character's codepoint in a specific charset. The following two functions support these conversions.
This function decodes a character that is assigned a code-point in charset, to the corresponding Emacs character, and returns it. If charset doesn't contain a character of that code point, the value is
nil. If code-point doesn't fit in a Lisp integer (see most-positive-fixnum), it can be specified as a cons cell(high.low), where low are the lower 16 bits of the value and high are the high 16 bits.
This function returns the code point assigned to the character char in charset. If the result does not fit in a Lisp integer, it is returned as a cons cell
(high.low)that fits the second argument ofdecode-charabove. If charset doesn't have a codepoint for char, the value isnil.
The following function comes in handy for applying a certain function to all or part of the characters in a charset:
Call function for characters in charset. function is called with two arguments. The first one is a cons cell
(from.to), where from and to indicate a range of characters contained in charset. The second argument passed to function is arg.By default, the range of codepoints passed to function includes all the characters in charset, but optional arguments from-code and to-code limit that to the range of characters between these two codepoints of charset. If either of them is
nil, it defaults to the first or last codepoint of charset, respectively.
Sometimes it is useful to find out which character set a particular character belongs to. One use for this is in determining which coding systems (see Coding Systems) are capable of representing all of the text in question; another is to determine the font(s) for displaying that text.
This function returns the charset of highest priority containing the character at position pos in the current buffer. If pos is omitted or
nil, it defaults to the current value of point. If pos is out of range, the value isnil.
This function returns a list of the character sets of highest priority that contain characters in the current buffer between positions beg and end.
The optional argument translation specifies a translation table to use for scanning the text (see Translation of Characters). If it is non-
nil, then each character in the region is translated through this table, and the value returned describes the translated characters instead of the characters actually in the buffer.
This function returns a list of character sets of highest priority that contain characters in string. It is just like
find-charset-region, except that it applies to the contents of string instead of part of the current buffer.
A translation table is a char-table (see Char-Tables) that specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems.
A translation table has two extra slots. The first is either
nil or a translation table that performs the reverse
translation; the second is the maximum number of characters to look up
for translating sequences of characters (see the description of
make-translation-table-from-alist below).
This function returns a translation table based on the argument translations. Each element of translations should be a list of elements of the form
(from.to); this says to translate the character from into to.The arguments and the forms in each argument are processed in order, and if a previous form already translates to to some other character, say to-alt, from is also translated to to-alt.
During decoding, the translation table's translations are applied to
the characters that result from ordinary decoding. If a coding system
has the property :decode-translation-table, that specifies the
translation table to use, or a list of translation tables to apply in
sequence. (This is a property of the coding system, as returned by
coding-system-get, not a property of the symbol that is the
coding system's name. See Basic Concepts of Coding Systems.) Finally, if
standard-translation-table-for-decode is non-nil, the
resulting characters are translated by that table.
During encoding, the translation table's translations are applied to
the characters in the buffer, and the result of translation is
actually encoded. If a coding system has property
:encode-translation-table, that specifies the translation table
to use, or a list of translation tables to apply in sequence. In
addition, if the variable standard-translation-table-for-encode
is non-nil, it specifies the translation table to use for
translating the result.
This is the default translation table for decoding. If a coding systems specifies its own translation tables, the table that is the value of this variable, if non-
nil, is applied after them.
This is the default translation table for encoding. If a coding systems specifies its own translation tables, the table that is the value of this variable, if non-
nil, is applied after them.
Self-inserting characters are translated through this translation table before they are inserted. Search commands also translate their input through this table, so they can compare more reliably with what's in the buffer.
This variable automatically becomes buffer-local when set.
This function returns a translation table made from vec that is an array of 256 elements to map bytes (values 0 through #xFF) to characters. Elements may be
nilfor untranslated bytes. The returned table has a translation table for reverse mapping in the first extra slot, and the value1in the second extra slot.This function provides an easy way to make a private coding system that maps each byte to a specific character. You can specify the returned table and the reverse translation table using the properties
:decode-translation-tableand:encode-translation-tablerespectively in the props argument todefine-coding-system.
This function is similar to
make-translation-tablebut returns a complex translation table rather than a simple one-to-one mapping. Each element of alist is of the form(from.to), where from and to are either characters or vectors specifying a sequence of characters. If from is a character, that character is translated to to (i.e. to a character or a character sequence). If from is a vector of characters, that sequence is translated to to. The returned table has a translation table for reverse mapping in the first extra slot, and the maximum length of all the from character sequences in the second extra slot.
When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives text from a subprocess, it normally performs character code conversion and end-of-line conversion as specified by a particular coding system.
How to define a coding system is an arcane matter, and is not documented here.
Character code conversion involves conversion between the internal representation of characters used inside Emacs and some other encoding. Emacs supports many different encodings, in that it can convert to and from them. For example, it can convert text to or from encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some cases, Emacs supports several alternative encodings for the same characters; for example, there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and KOI8.
Every coding system specifies a particular set of character code
conversions, but the coding system undecided is special: it
leaves the choice unspecified, to be chosen heuristically for each
file, based on the file's data.
In general, a coding system doesn't guarantee roundtrip identity: decoding a byte sequence using coding system, then encoding the resulting text in the same coding system, can produce a different byte sequence. But some coding systems do guarantee that the byte sequence will be the same as what you originally decoded. Here are a few examples:
iso-8859-1, utf-8, big5, shift_jis, euc-jp
Encoding buffer text and then decoding the result can also fail to reproduce the original text. For instance, if you encode a character with a coding system which does not support that character, the result is unpredictable, and thus decoding it using the same coding system may produce a different text. Currently, Emacs can't report errors that result from encoding unsupported characters.
End of line conversion handles three different conventions used on various systems for representing end of line in files. The Unix convention, used on GNU and Unix systems, is to use the linefeed character (also called newline). The DOS convention, used on MS-Windows and MS-DOS systems, is to use a carriage-return and a linefeed at the end of a line. The Mac convention is to use just carriage-return.
Base coding systems such as latin-1 leave the end-of-line
conversion unspecified, to be chosen based on the data. Variant
coding systems such as latin-1-unix, latin-1-dos and
latin-1-mac specify the end-of-line conversion explicitly as
well. Most base coding systems have three corresponding variants whose
names are formed by adding ‘-unix’, ‘-dos’ and ‘-mac’.
The coding system raw-text is special in that it prevents
character code conversion, and causes the buffer visited with this
coding system to be a unibyte buffer. For historical reasons, you can
save both unibyte and multibyte text with this coding system. When
you use raw-text to encode multibyte text, it does perform one
character code conversion: it converts eight-bit characters to their
single-byte external representation. raw-text does not specify
the end-of-line conversion, allowing that to be determined as usual by
the data, and has the usual three variants which specify the
end-of-line conversion.
no-conversion (and its alias binary) is equivalent to
raw-text-unix: it specifies no conversion of either character
codes or end-of-line.
The coding system utf-8-emacs specifies that the data is
represented in the internal Emacs encoding (see Text Representations). This is like raw-text in that no code
conversion happens, but different in that the result is multibyte
data. The name emacs-internal is an alias for
utf-8-emacs.
This function returns the specified property of the coding system coding-system. Most coding system properties exist for internal purposes, but one that you might find useful is
:mime-charset. That property's value is the name used in MIME for the character coding which this coding system can read and write. Examples:(coding-system-get 'iso-latin-1 :mime-charset) ⇒ iso-8859-1 (coding-system-get 'iso-2022-cn :mime-charset) ⇒ iso-2022-cn (coding-system-get 'cyrillic-koi8 :mime-charset) ⇒ koi8-rThe value of the
:mime-charsetproperty is also defined as an alias for the coding system.
This function returns the list of aliases of coding-system.
The principal purpose of coding systems is for use in reading and
writing files. The function insert-file-contents uses a coding
system to decode the file data, and write-region uses one to
encode the buffer contents.
You can specify the coding system to use either explicitly
(see Specifying Coding Systems), or implicitly using a default
mechanism (see Default Coding Systems). But these methods may not
completely specify what to do. For example, they may choose a coding
system such as undefined which leaves the character code
conversion to be determined from the data. In these cases, the I/O
operation finishes the job of choosing a coding system. Very often
you will want to find out afterwards which coding system was chosen.
This buffer-local variable records the coding system used for saving the buffer and for writing part of the buffer with
write-region. If the text to be written cannot be safely encoded using the coding system specified by this variable, these operations select an alternative encoding by calling the functionselect-safe-coding-system(see User-Chosen Coding Systems). If selecting a different encoding requires to ask the user to specify a coding system,buffer-file-coding-systemis updated to the newly selected coding system.
buffer-file-coding-systemdoes not affect sending text to a subprocess.
This variable specifies the coding system for saving the buffer (by overriding
buffer-file-coding-system). Note that it is not used forwrite-region.When a command to save the buffer starts out to use
buffer-file-coding-system(orsave-buffer-coding-system), and that coding system cannot handle the actual text in the buffer, the command asks the user to choose another coding system (by callingselect-safe-coding-system). After that happens, the command also updatesbuffer-file-coding-systemto represent the coding system that the user specified.
I/O operations for files and subprocesses set this variable to the coding system name that was used. The explicit encoding and decoding functions (see Explicit Encoding) set it too.
Warning: Since receiving subprocess output sets this variable, it can change whenever Emacs waits; therefore, you should copy the value shortly after the function call that stores the value you are interested in.
The variable selection-coding-system specifies how to encode
selections for the window system. See Window System Selections.
The variable
file-name-coding-systemspecifies the coding system to use for encoding file names. Emacs encodes file names using that coding system for all file operations. Iffile-name-coding-systemisnil, Emacs uses a default coding system determined by the selected language environment. In the default language environment, any non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation.
Warning: if you change file-name-coding-system (or
the language environment) in the middle of an Emacs session, problems
can result if you have already visited files whose names were encoded
using the earlier coding system and are handled differently under the
new coding system. If you try to save one of these buffers under the
visited file name, saving may use the wrong file name, or it may get
an error. If such a problem happens, use C-x C-w to specify a
new file name for that buffer.
Here are the Lisp facilities for working with coding systems:
This function returns a list of all coding system names (symbols). If base-only is non-
nil, the value includes only the base coding systems. Otherwise, it includes alias and variant coding systems as well.
This function returns
tif object is a coding system name ornil.
This function checks the validity of coding-system. If that is valid, it returns coding-system. If coding-system is
nil, the function returnnil. For any other values, it signals an error whoseerror-symboliscoding-system-error(see signal).
This function returns the type of end-of-line (a.k.a. eol) conversion used by coding-system. If coding-system specifies a certain eol conversion, the return value is an integer 0, 1, or 2, standing for
unix,dos, andmac, respectively. If coding-system doesn't specify eol conversion explicitly, the return value is a vector of coding systems, each one with one of the possible eol conversion types, like this:(coding-system-eol-type 'latin-1) ⇒ [latin-1-unix latin-1-dos latin-1-mac]If this function returns a vector, Emacs will decide, as part of the text encoding or decoding process, what eol conversion to use. For decoding, the end-of-line format of the text is auto-detected, and the eol conversion is set to match it (e.g., DOS-style CRLF format will imply
doseol conversion). For encoding, the eol conversion is taken from the appropriate default coding system (e.g., default value ofbuffer-file-coding-systemforbuffer-file-coding-system), or from the default eol conversion appropriate for the underlying platform.
This function returns a coding system which is like coding-system except for its eol conversion, which is specified by
eol-type. eol-type should beunix,dos,mac, ornil. If it isnil, the returned coding system determines the end-of-line conversion from the data.eol-type may also be 0, 1 or 2, standing for
unix,dosandmac, respectively.
This function returns a coding system which uses the end-of-line conversion of eol-coding, and the text conversion of text-coding. If text-coding is
nil, it returnsundecided, or one of its variants according to eol-coding.
This function returns a list of coding systems that could be used to encode a text between from and to. All coding systems in the list can safely encode any multibyte characters in that portion of the text.
If the text contains no multibyte characters, the function returns the list
(undecided).
This function returns a list of coding systems that could be used to encode the text of string. All coding systems in the list can safely encode any multibyte characters in string. If the text contains no multibyte characters, this returns the list
(undecided).
This function returns a list of coding systems that could be used to encode all the character sets in the list charsets.
This function checks whether coding systems in the list
coding-system-listcan encode all the characters in the region between start and end. If all of the coding systems in the list can encode the specified text, the function returnsnil. If some coding systems cannot encode some of the characters, the value is an alist, each element of which has the form(coding-system1 pos1 pos2...), meaning that coding-system1 cannot encode characters at buffer positions pos1, pos2, ....start may be a string, in which case end is ignored and the returned value references string indices instead of buffer positions.
This function chooses a plausible coding system for decoding the text from start to end. This text should be a byte sequence, i.e. unibyte text or multibyte text with only ASCII and eight-bit characters (see Explicit Encoding).
Normally this function returns a list of coding systems that could handle decoding the text that was scanned. They are listed in order of decreasing priority. But if highest is non-
nil, then the return value is just one coding system, the one that is highest in priority.If the region contains only ASCII characters except for such ISO-2022 control characters ISO-2022 as
ESC, the value isundecidedor(undecided), or a variant specifying end-of-line conversion, if that can be deduced from the text.If the region contains null bytes, the value is
no-conversion, even if the region contains text encoded in some coding system.
This function is like
detect-coding-regionexcept that it operates on the contents of string instead of bytes in the buffer.
If this variable has a non-
nilvalue, null bytes are ignored when detecting the encoding of a region or a string. This allows to correctly detect the encoding of text that contains null bytes, such as Info files with Index nodes.
If this variable has a non-
nilvalue, ISO-2022 escape sequences are ignored when detecting the encoding of a region or a string. The result is that no text is ever detected as encoded in some ISO-2022 encoding, and all escape sequences become visible in a buffer. Warning: Use this variable with extreme caution, because many files in the Emacs distribution use ISO-2022 encoding.
This function returns the list of character sets (see Character Sets) supported by coding-system. Some coding systems that support too many character sets to list them all yield special values:
- If coding-system supports all the ISO-2022 charsets, the value is
iso-2022.- If coding-system supports all Emacs characters, the value is
(emacs).- If coding-system supports all emacs-mule characters, the value is
emacs-mule.- If coding-system supports all Unicode characters, the value is
(unicode).
See Process Information, in
particular the description of the functions
process-coding-system and set-process-coding-system, for
how to examine or set the coding systems used for I/O to a subprocess.
This function selects a coding system for encoding specified text, asking the user to choose if necessary. Normally the specified text is the text in the current buffer between from and to. If from is a string, the string specifies the text to encode, and to is ignored.
If the specified text includes raw bytes (see Text Representations),
select-safe-coding-systemsuggestsraw-textfor its encoding.If default-coding-system is non-
nil, that is the first coding system to try; if that can handle the text,select-safe-coding-systemreturns that coding system. It can also be a list of coding systems; then the function tries each of them one by one. After trying all of them, it next tries the current buffer's value ofbuffer-file-coding-system(if it is notundecided), then the default value ofbuffer-file-coding-systemand finally the user's most preferred coding system, which the user can set using the commandprefer-coding-system(see Recognizing Coding Systems).If one of those coding systems can safely encode all the specified text,
select-safe-coding-systemchooses it and returns it. Otherwise, it asks the user to choose from a list of coding systems which can encode all the text, and returns the user's choice.default-coding-system can also be a list whose first element is t and whose other elements are coding systems. Then, if no coding system in the list can handle the text,
select-safe-coding-systemqueries the user immediately, without trying any of the three alternatives described above.The optional argument accept-default-p, if non-
nil, should be a function to determine whether a coding system selected without user interaction is acceptable.select-safe-coding-systemcalls this function with one argument, the base coding system of the selected coding system. If accept-default-p returnsnil,select-safe-coding-systemrejects the silently selected coding system, and asks the user to select a coding system from a list of possible candidates.If the variable
select-safe-coding-system-accept-default-pis non-nil, it should be a function taking a single argument. It is used in place of accept-default-p, overriding any value supplied for this argument.As a final step, before returning the chosen coding system,
select-safe-coding-systemchecks whether that coding system is consistent with what would be selected if the contents of the region were read from a file. (If not, this could lead to data corruption in a file subsequently re-visited and edited.) Normally,select-safe-coding-systemusesbuffer-file-nameas the file for this purpose, but if file is non-nil, it uses that file instead (this can be relevant forwrite-regionand similar functions). If it detects an apparent inconsistency,select-safe-coding-systemqueries the user before selecting the coding system.
Here are two functions you can use to let the user specify a coding system, with completion. See Completion.
This function reads a coding system using the minibuffer, prompting with string prompt, and returns the coding system name as a symbol. If the user enters null input, default specifies which coding system to return. It should be a symbol or a string.
This function reads a coding system using the minibuffer, prompting with string prompt, and returns the coding system name as a symbol. If the user tries to enter null input, it asks the user to try again. See Coding Systems.
This section describes variables that specify the default coding system for certain files or when running certain subprograms, and the function that I/O operations use to access them.
The idea of these variables is that you set them once and for all to the
defaults you want, and then do not change them again. To specify a
particular coding system for a particular operation in a Lisp program,
don't change these variables; instead, override them using
coding-system-for-read and coding-system-for-write
(see Specifying Coding Systems).
This variable is an alist of text patterns and corresponding coding systems. Each element has the form
(regexp.coding-system); a file whose first few kilobytes match regexp is decoded with coding-system when its contents are read into a buffer. The settings in this alist take priority overcoding:tags in the files and the contents offile-coding-system-alist(see below). The default value is set so that Emacs automatically recognizes mail files in Babyl format and reads them with no code conversions.
This variable is an alist that specifies the coding systems to use for reading and writing particular files. Each element has the form
(pattern.coding), where pattern is a regular expression that matches certain file names. The element applies to file names that match pattern.The cdr of the element, coding, should be either a coding system, a cons cell containing two coding systems, or a function name (a symbol with a function definition). If coding is a coding system, that coding system is used for both reading the file and writing it. If coding is a cons cell containing two coding systems, its car specifies the coding system for decoding, and its cdr specifies the coding system for encoding.
If coding is a function name, the function should take one argument, a list of all arguments passed to
find-operation-coding-system. It must return a coding system or a cons cell containing two coding systems. This value has the same meaning as described above.If coding (or what returned by the above function) is
undecided, the normal code-detection is performed.
This variable is an alist that specifies the coding systems to use for reading and writing particular files. Its form is like that of
file-coding-system-alist, but, unlike the latter, this variable takes priority over anycoding:tags in the file.
This variable is an alist specifying which coding systems to use for a subprocess, depending on which program is running in the subprocess. It works like
file-coding-system-alist, except that pattern is matched against the program name used to start the subprocess. The coding system or systems specified in this alist are used to initialize the coding systems used for I/O to the subprocess, but you can specify other coding systems later usingset-process-coding-system.
Warning: Coding systems such as undecided, which
determine the coding system from the data, do not work entirely reliably
with asynchronous subprocess output. This is because Emacs handles
asynchronous subprocess output in batches, as it arrives. If the coding
system leaves the character code conversion unspecified, or leaves the
end-of-line conversion unspecified, Emacs must try to detect the proper
conversion from one batch at a time, and this does not always work.
Therefore, with an asynchronous subprocess, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion—that is, one like latin-1-unix,
rather than undecided or latin-1.
This variable is an alist that specifies the coding system to use for network streams. It works much like
file-coding-system-alist, with the difference that the pattern in an element may be either a port number or a regular expression. If it is a regular expression, it is matched against the network service name used to open the network stream.
This variable specifies the coding systems to use for subprocess (and network stream) input and output, when nothing else specifies what to do.
The value should be a cons cell of the form
(input-coding.output-coding). Here input-coding applies to input from the subprocess, and output-coding applies to output to it.
This variable holds a list of functions that try to determine a coding system for a file based on its undecoded contents.
Each function in this list should be written to look at text in the current buffer, but should not modify it in any way. The buffer will contain undecoded text of parts of the file. Each function should take one argument, size, which tells it how many characters to look at, starting from point. If the function succeeds in determining a coding system for the file, it should return that coding system. Otherwise, it should return
nil.If a file has a ‘coding:’ tag, that takes precedence, so these functions won't be called.
This function tries to determine a suitable coding system for filename. It examines the buffer visiting the named file, using the variables documented above in sequence, until it finds a match for one of the rules specified by these variables. It then returns a cons cell of the form
(coding.source), where coding is the coding system to use and source is a symbol, one ofauto-coding-alist,auto-coding-regexp-alist,:coding, orauto-coding-functions, indicating which one supplied the matching rule. The value:codingmeans the coding system was specified by thecoding:tag in the file (see coding tag). The order of looking for a matching rule isauto-coding-alistfirst, thenauto-coding-regexp-alist, then thecoding:tag, and lastlyauto-coding-functions. If no matching rule was found, the function returnsnil.The second argument size is the size of text, in characters, following point. The function examines text only within size characters after point. Normally, the buffer should be positioned at the beginning when this function is called, because one of the places for the
coding:tag is the first one or two lines of the file; in that case, size should be the size of the buffer.
This function returns a suitable coding system for file filename. It uses
find-auto-codingto find the coding system. If no coding system could be determined, the function returnsnil. The meaning of the argument size is like infind-auto-coding.
This function returns the coding system to use (by default) for performing operation with arguments. The value has this form:
(decoding-system . encoding-system)The first element, decoding-system, is the coding system to use for decoding (in case operation does decoding), and encoding-system is the coding system for encoding (in case operation does encoding).
The argument operation is a symbol, one of
write-region,start-process,call-process,call-process-region,insert-file-contents, oropen-network-stream. These are the names of the Emacs I/O primitives that can do character code and eol conversion.The remaining arguments should be the same arguments that might be given to the corresponding I/O primitive. Depending on the primitive, one of those arguments is selected as the target. For example, if operation does file I/O, whichever argument specifies the file name is the target. For subprocess primitives, the process name is the target. For
open-network-stream, the target is the service name or port number.Depending on operation, this function looks up the target in
file-coding-system-alist,process-coding-system-alist, ornetwork-coding-system-alist. If the target is found in the alist,find-operation-coding-systemreturns its association in the alist; otherwise it returnsnil.If operation is
insert-file-contents, the argument corresponding to the target may be a cons cell of the form(filename.buffer)). In that case, filename is a file name to look up infile-coding-system-alist, and buffer is a buffer that contains the file's contents (not yet decoded). Iffile-coding-system-alistspecifies a function to call for this file, and that function needs to examine the file's contents (as it usually does), it should examine the contents of buffer instead of reading the file.
You can specify the coding system for a specific operation by binding
the variables coding-system-for-read and/or
coding-system-for-write.
If this variable is non-
nil, it specifies the coding system to use for reading a file, or for input from a synchronous subprocess.It also applies to any asynchronous subprocess or network stream, but in a different way: the value of
coding-system-for-readwhen you start the subprocess or open the network stream specifies the input decoding method for that subprocess or network stream. It remains in use for that subprocess or network stream unless and until overridden.The right way to use this variable is to bind it with
letfor a specific I/O operation. Its global value is normallynil, and you should not globally set it to any other value. Here is an example of the right way to use the variable:;; Read the file with no character code conversion. ;; Assume crlf represents end-of-line. (let ((coding-system-for-read 'emacs-mule-dos)) (insert-file-contents filename))When its value is non-
nil, this variable takes precedence over all other methods of specifying a coding system to use for input, includingfile-coding-system-alist,process-coding-system-alistandnetwork-coding-system-alist.
This works much like
coding-system-for-read, except that it applies to output rather than input. It affects writing to files, as well as sending output to subprocesses and net connections.When a single operation does both input and output, as do
call-process-regionandstart-process, bothcoding-system-for-readandcoding-system-for-writeaffect it.
When this variable is non-
nil, no end-of-line conversion is done, no matter which coding system is specified. This applies to all the Emacs I/O and subprocess primitives, and to the explicit encoding and decoding functions (see Explicit Encoding).
Sometimes, you need to prefer several coding systems for some
operation, rather than fix a single one. Emacs lets you specify a
priority order for using coding systems. This ordering affects the
sorting of lists of coding sysems returned by functions such as
find-coding-systems-region (see Lisp and Coding Systems).
This function returns the list of coding systems in the order of their current priorities. Optional argument highestp, if non-
nil, means return only the highest priority coding system.
This function puts coding-systems at the beginning of the priority list for coding systems, thus making their priority higher than all the rest.
This macro execute body, like
progndoes (see progn), with coding-systems at the front of the priority list for coding systems. coding-systems should be a list of coding systems to prefer during execution of body.
All the operations that transfer text in and out of Emacs have the ability to use a coding system to encode or decode the text. You can also explicitly encode and decode text using the functions in this section.
The result of encoding, and the input to decoding, are not ordinary text. They logically consist of a series of byte values; that is, a series of ASCII and eight-bit characters. In unibyte buffers and strings, these characters have codes in the range 0 through #xFF (255). In a multibyte buffer or string, eight-bit characters have character codes higher than #xFF (see Text Representations), but Emacs transparently converts them to their single-byte values when you encode or decode such text.
The usual way to read a file into a buffer as a sequence of bytes, so
you can decode the contents explicitly, is with
insert-file-contents-literally (see Reading from Files);
alternatively, specify a non-nil rawfile argument when
visiting a file with find-file-noselect. These methods result in
a unibyte buffer.
The usual way to use the byte sequence that results from explicitly
encoding text is to copy it to a file or process—for example, to write
it with write-region (see Writing to Files), and suppress
encoding by binding coding-system-for-write to
no-conversion.
Here are the functions to perform explicit encoding or decoding. The
encoding functions produce sequences of bytes; the decoding functions
are meant to operate on sequences of bytes. All of these functions
discard text properties. They also set last-coding-system-used
to the precise coding system they used.
This command encodes the text from start to end according to coding system coding-system. Normally, the encoded text replaces the original text in the buffer, but the optional argument destination can change that. If destination is a buffer, the encoded text is inserted in that buffer after point (point does not move); if it is
t, the command returns the encoded text as a unibyte string without inserting it.If encoded text is inserted in some buffer, this command returns the length of the encoded text.
The result of encoding is logically a sequence of bytes, but the buffer remains multibyte if it was multibyte before, and any 8-bit bytes are converted to their multibyte representation (see Text Representations).
Do not use
undecidedfor coding-system when encoding text, since that may lead to unexpected results. Instead, useselect-safe-coding-system(see select-safe-coding-system) to suggest a suitable encoding, if there's no obvious pertinent value for coding-system.
This function encodes the text in string according to coding system coding-system. It returns a new string containing the encoded text, except when nocopy is non-
nil, in which case the function may return string itself if the encoding operation is trivial. The result of encoding is a unibyte string.
This command decodes the text from start to end according to coding system coding-system. To make explicit decoding useful, the text before decoding ought to be a sequence of byte values, but both multibyte and unibyte buffers are acceptable (in the multibyte case, the raw byte values should be represented as eight-bit characters). Normally, the decoded text replaces the original text in the buffer, but the optional argument destination can change that. If destination is a buffer, the decoded text is inserted in that buffer after point (point does not move); if it is
t, the command returns the decoded text as a multibyte string without inserting it.If decoded text is inserted in some buffer, this command returns the length of the decoded text.
This command puts a
charsettext property on the decoded text. The value of the property states the character set used to decode the original text.
This function decodes the text in string according to coding-system. It returns a new string containing the decoded text, except when nocopy is non-
nil, in which case the function may return string itself if the decoding operation is trivial. To make explicit decoding useful, the contents of string ought to be a unibyte string with a sequence of byte values, but a multibyte string is also acceptable (assuming it contains 8-bit bytes in their multibyte form).If optional argument buffer specifies a buffer, the decoded text is inserted in that buffer after point (point does not move). In this case, the return value is the length of the decoded text.
This function puts a
charsettext property on the decoded text. The value of the property states the character set used to decode the original text:(decode-coding-string "Gr\374ss Gott" 'latin-1) ⇒ #("Grüss Gott" 0 9 (charset iso-8859-1))
This function decodes the text from from to to as if it were being read from file filename using
insert-file-contentsusing the rest of the arguments provided.The normal way to use this function is after reading text from a file without decoding, if you decide you would rather have decoded it. Instead of deleting the text and reading it again, this time with decoding, you can call this function.
Emacs can decode keyboard input using a coding system, and encode
terminal output. This is useful for terminals that transmit or
display text using a particular encoding such as Latin-1. Emacs does
not set last-coding-system-used for encoding or decoding of
terminal I/O.
This function returns the coding system that is in use for decoding keyboard input from terminal—or
nilif no coding system is to be used for that terminal. If terminal is omitted ornil, it means the selected frame's terminal. See Multiple Terminals.
This command specifies coding-system as the coding system to use for decoding keyboard input from terminal. If coding-system is
nil, that means do not decode keyboard input. If terminal is a frame, it means that frame's terminal; if it isnil, that means the currently selected frame's terminal. See Multiple Terminals.
This function returns the coding system that is in use for encoding terminal output from terminal—or
nilif the output is not encoded. If terminal is a frame, it means that frame's terminal; if it isnil, that means the currently selected frame's terminal.
This command specifies coding-system as the coding system to use for encoding terminal output from terminal. If coding-system is
nil, terminal output is not encoded. If terminal is a frame, it means that frame's terminal; if it isnil, that means the currently selected frame's terminal.
On MS-DOS and Microsoft Windows, Emacs guesses the appropriate end-of-line conversion for a file by looking at the file's name. This feature classifies files as text files and binary files. By “binary file” we mean a file of literal byte values that are not necessarily meant to be characters; Emacs does no end-of-line conversion and no character code conversion for them. On the other hand, the bytes in a text file are intended to represent characters; when you create a new file whose name implies that it is a text file, Emacs uses DOS end-of-line conversion.
This variable, automatically buffer-local in each buffer, records the file type of the buffer's visited file. When a buffer does not specify a coding system with
buffer-file-coding-system, this variable is used to determine which coding system to use when writing the contents of the buffer. It should benilfor text,tfor binary. If it ist, the coding system isno-conversion. Otherwise,undecided-dosis used.Normally this variable is set by visiting a file; it is set to
nilif the file was visited without any actual conversion.Its default value is used to decide how to handle files for which
file-name-buffer-file-type-alistsays nothing about the type: If the default value is non-nil, then these files are treated as binary: the coding systemno-conversionis used. Otherwise, nothing special is done for them—the coding system is deduced solely from the file contents, in the usual Emacs fashion.
This variable holds an alist for recognizing text and binary files. Each element has the form (regexp . type), where regexp is matched against the file name, and type may be
nilfor text,tfor binary, or a function to call to compute which. If it is a function, then it is called with a single argument (the file name) and should returntornil.When running on MS-DOS or MS-Windows, Emacs checks this alist to decide which coding system to use when reading a file. For a text file,
undecided-dosis used. For a binary file,no-conversionis used.If no element in this alist matches a given file name, then the default value of
buffer-file-typesays how to treat the file.
Input methods provide convenient ways of entering non-ASCII characters from the keyboard. Unlike coding systems, which translate non-ASCII characters to and from encodings meant to be read by programs, input methods provide human-friendly commands. (See Input Methods, for information on how users use input methods to enter text.) How to define input methods is not yet documented in this manual, but here we describe how to use them.
Each input method has a name, which is currently a string; in the future, symbols may also be usable as input method names.
This variable holds the name of the input method now active in the current buffer. (It automatically becomes local in each buffer when set in any fashion.) It is
nilif no input method is active in the buffer now.
This variable holds the default input method for commands that choose an input method. Unlike
current-input-method, this variable is normally global.
This command activates input method input-method for the current buffer. It also sets
default-input-methodto input-method. If input-method isnil, this command deactivates any input method for the current buffer.
This function reads an input method name with the minibuffer, prompting with prompt. If default is non-
nil, that is returned by default, if the user enters empty input. However, if inhibit-null is non-nil, empty input signals an error.The returned value is a string.
This variable defines all the supported input methods. Each element defines one input method, and should have the form:
(input-method language-env activate-func title description args...)Here input-method is the input method name, a string; language-env is another string, the name of the language environment this input method is recommended for. (That serves only for documentation purposes.)
activate-func is a function to call to activate this method. The args, if any, are passed as arguments to activate-func. All told, the arguments to activate-func are input-method and the args.
title is a string to display in the mode line while this method is active. description is a string describing this method and what it is good for.
The fundamental interface to input methods is through the
variable input-method-function. See Reading One Event,
and Invoking the Input Method.
POSIX defines a concept of “locales” which control which language to use in language-related features. These Emacs variables control how Emacs interacts with these features.
This variable specifies the coding system to use for decoding system error messages and—on X Window system only—keyboard input, for encoding the format argument to
format-time-string, and for decoding the return value offormat-time-string.
This variable specifies the locale to use for generating system error messages. Changing the locale can cause messages to come out in a different language or in a different orthography. If the variable is
nil, the locale is specified by environment variables in the usual POSIX fashion.
This variable specifies the locale to use for formatting time values. Changing the locale can cause messages to appear according to the conventions of a different language. If the variable is
nil, the locale is specified by environment variables in the usual POSIX fashion.
This function returns locale data item for the current POSIX locale, if available. item should be one of these symbols:
codeset- Return the character set as a string (locale item
CODESET).days- Return a 7-element vector of day names (locale items
DAY_1throughDAY_7);months- Return a 12-element vector of month names (locale items
MON_1throughMON_12).paper- Return a list
(width height)for the default paper size measured in millimeters (locale itemsPAPER_WIDTHandPAPER_HEIGHT).If the system can't provide the requested information, or if item is not one of those symbols, the value is
nil. All strings in the return value are decoded usinglocale-coding-system. See Locales, for more information about locales and locale items.
GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the match data to determine which text matched the whole regular expression or various portions of it.
The ‘skip-chars...’ functions also perform a kind of searching. See Skipping Characters. To search for changes in character properties, see Property Search.
These are the primitive functions for searching through the text in a
buffer. They are meant for use in programs, but you may call them
interactively. If you do so, they prompt for the search string; the
arguments limit and noerror are nil, and repeat
is 1.
These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. See Text Representations.
This function searches forward from point for an exact match for string. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on noerror (see below).
In the following example, point is initially at the beginning of the line. Then
(search-forward "fox")moves point after the last letter of ‘fox’:---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") ⇒ 20 ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ----------The argument limit specifies the upper bound to the search. (It must be a position in the current buffer.) No match extending after that position is accepted. If limit is omitted or
nil, it defaults to the end of the accessible portion of the buffer.What happens when the search fails depends on the value of noerror. If noerror is
nil, asearch-failederror is signaled. If noerror ist,search-forwardreturnsniland does nothing. If noerror is neithernilnort, thensearch-forwardmoves point to the upper bound and returnsnil. (It would be more consistent now to return the new position of point in that case, but some existing programs may depend on a value ofnil.)The argument noerror only affects valid searches which fail to find a match. Invalid arguments cause errors regardless of noerror.
If repeat is supplied (it must be a positive number), then the search is repeated that many times (each time starting at the end of the previous time's match). If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails, with results depending on the value of noerror, as described above.
This function searches backward from point for string. It is just like
search-forwardexcept that it searches backwards and leaves point at the beginning of the match.
This function searches forward from point for a “word” match for string. If it finds a match, it sets point to the end of the match found, and returns the new value of point.
Word matching regards string as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word ‘ball’ does not match the word ‘balls’), but the details of punctuation and spacing are ignored (searching for ‘ball boy’ does match ‘ball. Boy!’).
In this example, point is initially at the beginning of the buffer; the search leaves it between the ‘y’ and the ‘!’.
---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") ⇒ 35 ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ----------If limit is non-
nil, it must be a position in the current buffer; it specifies the upper bound to the search. The match found must not extend after that position.If noerror is
nil, thenword-search-forwardsignals an error if the search fails. If noerror ist, then it returnsnilinstead of signaling an error. If noerror is neithernilnort, it moves point to limit (or the end of the accessible portion of the buffer) and returnsnil.If repeat is non-
nil, then the search is repeated that many times. Point is positioned at the end of the last match.
This command is identical to
word-search-forward, except that the end ofstringneed not match a word boundary unless it ends in whitespace. For instance, searching for ‘ball boy’ matches ‘ball boyee’, but does not match ‘aball boy’.
This function searches backward from point for a word match to string. This function is just like
word-search-forwardexcept that it searches backward and normally leaves point at the beginning of the match.
This command is identical to
word-search-backward, except that the end ofstringneed not match a word boundary unless it ends in whitespace.
By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for ‘FOO’, then ‘Foo’ or ‘foo’ is also considered a match. This applies to regular expressions, too; thus, ‘[aB]’ would match ‘a’ or ‘A’ or ‘b’ or ‘B’.
If you do not want this feature, set the variable
case-fold-search to nil. Then all letters must match
exactly, including case. This is a buffer-local variable; altering the
variable affects only the current buffer. (See Intro to Buffer-Local.) Alternatively, you may change the default value of
case-fold-search.
Note that the user-level incremental search feature handles case distinctions differently. When the search string contains only lower case letters, the search ignores case, but when the search string contains one or more upper case letters, the search becomes case-sensitive. But this has nothing to do with the searching functions used in Lisp code.
This buffer-local variable determines whether searches should ignore case. If the variable is
nilthey do not ignore case; otherwise they do ignore case.
This variable determines whether the higher level replacement functions should preserve case. If the variable is
nil, that means to use the replacement text verbatim. A non-nilvalue means to convert the case of the replacement text according to the text being replaced.This variable is used by passing it as an argument to the function
replace-match. See Replacing Match.
A regular expression, or regexp for short, is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them.
For convenient interactive development of regular expressions, you can use the M-x re-builder command. It provides a convenient interface for creating regular expressions, by giving immediate visual feedback in a separate buffer. As you edit the regexp, all its matches in the target buffer are highlighted. Each parenthesized sub-expression of the regexp is shown in a distinct face, which makes it easier to verify even very complex regexps.
Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are ‘.’, ‘*’, ‘+’, ‘?’, ‘[’, ‘^’, ‘$’, and ‘\’; no new special characters will be defined in the future. The character ‘]’ is special if it ends a character alternative (see later). The character ‘-’ is special inside a character alternative. A ‘[:’ and balancing ‘:]’ enclose a character class inside a character alternative. Any other character appearing in a regular expression is ordinary, unless a ‘\’ precedes it.
For example, ‘f’ is not a special character, so it is ordinary, and therefore ‘f’ is a regular expression that matches the string ‘f’ and no other string. (It does not match the string ‘fg’, but it does match a part of that string.) Likewise, ‘o’ is a regular expression that matches only ‘o’.
Any two regular expressions a and b can be concatenated. The result is a regular expression that matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.
As a simple example, we can concatenate the regular expressions ‘f’ and ‘o’ to get the regular expression ‘fo’, which matches only the string ‘fo’. Still trivial. To do something more powerful, you need to use one of the special regular expression constructs.
Here is a list of the characters that are special in a regular expression.
‘*’ always applies to the smallest possible preceding expression. Thus, ‘fo*’ has a repeating ‘o’, not a repeating ‘fo’. It matches ‘f’, ‘fo’, ‘foo’, and so on.
The matcher processes a ‘*’ construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the ‘*’-modified construct in the hope that that will make it possible to match the rest of the pattern. For example, in matching ‘ca*ar’ against the string ‘caaar’, the ‘a*’ first tries to match all three ‘a’s; but the rest of the pattern is ‘ar’ and there is only ‘r’ left to match, so this try fails. The next alternative is for ‘a*’ to match only two ‘a’s. With this choice, the rest of the regexp matches successfully.
Warning: Nested repetition operators can run for an
indefinitely long time, if they lead to ambiguous matching. For
example, trying to match the regular expression ‘\(x+y*\)*a’
against the string ‘xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz’ could
take hours before it ultimately fails. Emacs must try each way of
grouping the ‘x’s before concluding that none of them can work.
Even worse, ‘\(x*\)*’ can match the null string in infinitely
many ways, so it causes an infinite loop. To avoid these problems,
check nested repetitions carefully, to make sure that they do not
cause combinatorial explosions in backtracking.
For example, the regular expression ‘c[ad]*a’ when applied to the
string ‘cdaaada’ matches the whole string; but the regular
expression ‘c[ad]*?a’, applied to that same string, matches just
‘cda’. (The smallest possible match here for ‘[ad]*?’ that
permits the whole expression to match is ‘d’.)
Thus, ‘[ad]’ matches either one ‘a’ or one ‘d’, and ‘[ad]*’ matches any string composed of just ‘a’s and ‘d’s (including the empty string). It follows that ‘c[ad]*r’ matches ‘cr’, ‘car’, ‘cdr’, ‘caddaar’, etc.
You can also include character ranges in a character alternative, by writing the starting and ending characters with a ‘-’ between them. Thus, ‘[a-z]’ matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in ‘[a-z$%.]’, which matches any lower case ASCII letter or ‘$’, ‘%’ or period.
Note that the usual regexp special characters are not special inside a character alternative. A completely different set of characters is special inside character alternatives: ‘]’, ‘-’ and ‘^’.
To include a ‘]’ in a character alternative, you must make it the first character. For example, ‘[]a]’ matches ‘]’ or ‘a’. To include a ‘-’, write ‘-’ as the first or last character of the character alternative, or put it after a range. Thus, ‘[]-]’ matches both ‘]’ and ‘-’.
To include ‘^’ in a character alternative, put it anywhere but at the beginning.
If a range starts with a unibyte character c and ends with a multibyte character c2, the range is divided into two parts: one is ‘c..?\377’, the other is ‘c1..c2’, where c1 is the first character of the charset to which c2 belongs.
A character alternative can also specify named character classes
(see Char Classes). This is a POSIX feature whose syntax is
‘[:class:]’. Using a character class is equivalent to
mentioning each of the characters in that class; but the latter is not
feasible in practice, since some classes include thousands of
different characters.
‘^’ is not special in a character alternative unless it is the first character. The character following the ‘^’ is treated as if it were first (in other words, ‘-’ and ‘]’ are not special there).
A complemented character alternative can match a newline, unless newline is
mentioned as one of the characters not to match. This is in contrast to
the handling of regexps in programs such as grep.
You can specify named character classes, just like in character
alternatives. For instance, ‘[^[:ascii:]]’ matches any
non-ASCII character. See Char Classes.
When matching a string instead of a buffer, ‘^’ matches at the beginning of the string or after a newline character.
For historical compatibility reasons, ‘^’ can be used only at the
beginning of the regular expression, or after ‘\(’, ‘\(?:’
or ‘\|’.
When matching a string instead of a buffer, ‘$’ matches at the end of the string or before a newline character.
For historical compatibility reasons, ‘$’ can be used only at the
end of the regular expression, or before ‘\)’ or ‘\|’.
Because ‘\’ quotes special characters, ‘\$’ is a regular expression that matches only ‘$’, and ‘\[’ is a regular expression that matches only ‘[’, and so on.
Note that ‘\’ also has special meaning in the read syntax of Lisp
strings (see 字符串类型), and must be quoted with ‘\’. For
example, the regular expression that matches the ‘\’ character is
‘\\’. To write a Lisp string that contains the characters
‘\\’, Lisp syntax requires you to quote each ‘\’ with another
‘\’. Therefore, the read syntax for a regular expression matching
‘\’ is "\\\\".
Please note: For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, ‘*foo’ treats ‘*’ as ordinary since there is no preceding expression on which the ‘*’ can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.
As a ‘\’ is not special inside a character alternative, it can
never remove the special meaning of ‘-’ or ‘]’. So you
should not quote these characters when they have no special meaning
either. This would not clarify anything, since backslashes can
legitimately precede these characters where they have special
meaning, as in ‘[^\]’ ("[^\\]" for Lisp string syntax),
which matches any single character except a backslash.
In practice, most ‘]’ that occur in regular expressions close a character alternative and hence are special. However, occasionally a regular expression may try to match a complex pattern of literal ‘[’ and ‘]’. In such situations, it sometimes may be necessary to carefully parse the regexp from the start to determine which square brackets enclose a character alternative. For example, ‘[^][]]’ consists of the complemented character alternative ‘[^][]’ (which matches any single character that is not a square bracket), followed by a literal ‘]’.
The exact rules are that at the beginning of a regexp, ‘[’ is special and ‘]’ not. This lasts until the first unquoted ‘[’, after which we are in a character alternative; ‘[’ is no longer special (except when it starts a character class) but ‘]’ is special, unless it immediately follows the special ‘[’ or that ‘[’ followed by a ‘^’. This lasts until the next special ‘]’ that does not end a character class. This ends the character alternative and restores the ordinary syntax of regular expressions; an unquoted ‘[’ is special again and a ‘]’ not.
Here is a table of the classes you can use in a character alternative, and what they mean:
case-fold-search is
non-nil, this also matches any upper-case letter.
case-fold-search is
non-nil, this also matches any lower-case letter.
For the most part, ‘\’ followed by any character matches only that character. However, there are several exceptions: certain two-character sequences starting with ‘\’ that have special meanings. (The character after the ‘\’ in such a sequence is always ordinary when used on its own.) Here is a table of the special ‘\’ constructs.
Thus, ‘foo\|bar’ matches either ‘foo’ or ‘bar’ but no other string.
‘\|’ applies to the largest possible surrounding expressions. Only a surrounding ‘\( ... \)’ grouping can limit the grouping power of ‘\|’.
If you need full backtracking capability to handle multiple uses of
‘\|’, use the POSIX regular expression functions (see POSIX Regexps).
For example, ‘c[ad]\{1,2\}r’ matches the strings ‘car’,
‘cdr’, ‘caar’, ‘cadr’, ‘cdar’, and ‘cddr’, and
nothing else.
‘\{0,1\}’ or ‘\{,1\}’ is equivalent to ‘?’.
‘\{0,\}’ or ‘\{,\}’ is equivalent to ‘*’.
‘\{1,\}’ is equivalent to ‘+’.
This last application is not a consequence of the idea of a
parenthetical grouping; it is a separate feature that was assigned as a
second meaning to the same ‘\( ... \)’ construct because, in
practice, there was usually no conflict between the two meanings. But
occasionally there is a conflict, and that led to the introduction of
shy groups.
Shy groups are also called non-capturing or unnumbered
groups.
In other words, after the end of a group, the matcher remembers the beginning and end of the text matched by that group. Later on in the regular expression you can use ‘\’ followed by digit to match that same text, whatever it may have been.
The strings matching the first nine grouping constructs appearing in the entire regular expression passed to a search or matching function are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use ‘\1’ through ‘\9’ to refer to the text matched by the corresponding grouping constructs.
For example, ‘\(.*\)\1’ matches any newline-free string that is composed of two identical halves. The ‘\(.*\)’ matches the first half, which may be anything, but the ‘\1’ that follows must match the same exact text.
If a ‘\( ... \)’ construct matches more than once (which can happen, for instance, if it is followed by ‘*’), only the last match is recorded.
If a particular grouping construct in the regular expression was never
matched—for instance, if it appears inside of an alternative that
wasn't used, or inside of a repetition that repeated zero times—then
the corresponding ‘\digit’ construct never matches
anything. To use an artificial example, ‘\(foo\(b*\)\|lose\)\2’
cannot match ‘lose’: the second alternative inside the larger
group matches it, but then ‘\2’ is undefined and can't match
anything. But it can match ‘foobb’, because the first
alternative matches ‘foob’ and ‘\2’ matches ‘b’.
The following regular expression constructs match the empty string—that is, they don't use up any characters—but whether they match depends on the context. For all, the beginning and end of the accessible portion of the buffer are treated as if they were the actual beginning and end of the buffer.
‘\b’ matches at the beginning or end of the buffer (or string)
regardless of what text appears next to it.
Not every string is a valid regular expression. For example, a string
that ends inside a character alternative without terminating ‘]’
is invalid, and so is a string that ends with a single ‘\’. If
an invalid regular expression is passed to any of the search functions,
an invalid-regexp error is signaled.
Here is a complicated regexp which was formerly used by Emacs to
recognize the end of a sentence together with any whitespace that
follows. (Nowadays Emacs uses a similar but more complex default
regexp constructed by the function sentence-end.
See Standard Regexps.)
First, we show the regexp as a string in Lisp syntax to distinguish spaces from tab characters. The string constant begins and ends with a double-quote. ‘\"’ stands for a double-quote as part of the string, ‘\\’ for a backslash as part of the string, ‘\t’ for a tab and ‘\n’ for a newline.
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
In contrast, if you evaluate this string, you will see the following:
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
⇒ "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[
]*"
In this output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be deciphered as follows:
[.?!][]\"')}]*\" is Lisp syntax for a double-quote in
a string. The ‘*’ at the end indicates that the immediately
preceding regular expression (a character alternative, in this case) may be
repeated zero or more times.
\\($\\| $\\|\t\\| \\)[ \t\n]*These functions operate on regular expressions.
This function returns a regular expression whose only exact match is string. Using this regular expression in
looking-atwill succeed only if the next characters in the buffer are string; using it in a search function will succeed if the text being searched contains string.This allows you to request an exact string match or search when calling a function that wants a regular expression.
(regexp-quote "^The cat$") ⇒ "\\^The cat\\$"One use of
regexp-quoteis to combine an exact string match with context described as a regular expression. For example, this searches for the string that is the value of string, surrounded by whitespace:(re-search-forward (concat "\\s-" (regexp-quote string) "\\s-"))
This function returns an efficient regular expression that will match any of the strings in the list strings. This is useful when you need to make matching or searching as fast as possible—for example, for Font Lock mode.
If the optional argument paren is non-
nil, then the returned regular expression is always enclosed by at least one parentheses-grouping construct. If paren iswords, then that construct is additionally surrounded by ‘\<’ and ‘\>’.This simplified definition of
regexp-optproduces a regular expression which is equivalent to the actual value (but not as efficient):(defun regexp-opt (strings paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren)))
This function returns the total number of grouping constructs (parenthesized expressions) in regexp. This does not include shy groups (see Regexp Backslash).
In GNU Emacs, you can search for the next match for a regular
expression either incrementally or not. For incremental search
commands, see Regular Expression Search. Here we describe only the search functions
useful in programs. The principal one is re-search-forward.
These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. See Text Representations.
This function searches forward in the current buffer for a string of text that is matched by the regular expression regexp. The function skips over any amount of text that is not matched by regexp, and leaves point at the end of the first match found. It returns the new value of point.
If limit is non-
nil, it must be a position in the current buffer. It specifies the upper bound to the search. No match extending after that position is accepted.If repeat is supplied, it must be a positive number; the search is repeated that many times; each repetition starts at the end of the previous match. If all these successive searches succeed, the search succeeds, moving point and returning its new value. Otherwise the search fails. What
re-search-forwarddoes when the search fails depends on the value of noerror:
nil- Signal a
search-failederror.t- Do nothing and return
nil.- anything else
- Move point to limit (or the end of the accessible portion of the buffer) and return
nil.In the following example, point is initially before the ‘T’. Evaluating the search call moves point to the end of that line (between the ‘t’ of ‘hat’ and the newline).
---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) ⇒ 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function searches backward in the current buffer for a string of text that is matched by the regular expression regexp, leaving point at the beginning of the first text found.
This function is analogous to
re-search-forward, but they are not simple mirror images.re-search-forwardfinds the match whose beginning is as close as possible to the starting point. Ifre-search-backwardwere a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible (and yet ends before the starting point). The reason for this is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position.A true mirror-image of
re-search-forwardwould require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that.
This function returns the index of the start of the first match for the regular expression regexp in string, or
nilif there is no match. If start is non-nil, the search starts at that index in string.For example,
(string-match "quick" "The quick brown fox jumped quickly.") ⇒ 4 (string-match "quick" "The quick brown fox jumped quickly." 8) ⇒ 27The index of the first character of the string is 0, the index of the second character is 1, and so on.
After this function returns, the index of the first character beyond the match is available as
(match-end 0). See Match Data.(string-match "quick" "The quick brown fox jumped quickly." 8) ⇒ 27 (match-end 0) ⇒ 32
This predicate function does what
string-matchdoes, but it avoids modifying the match data.
This function determines whether the text in the current buffer directly following point matches the regular expression regexp. “Directly following” means precisely that: the search is “anchored” and it can succeed only starting with the first character following point. The result is
tif so,nilotherwise.This function does not move point, but it updates the match data, which you can access using
match-beginningandmatch-end. See Match Data. If you need to test for a match without modifying the match data, uselooking-at-p, described below.In this example, point is located directly before the ‘T’. If it were anywhere else, the result would be
nil.---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") ⇒ t
This function returns
tif regexp matches text before point, ending at point, andnilotherwise.Because regular expression matching works only going forward, this is implemented by searching backwards from point for a match that ends at point. That can be quite slow if it has to search a long distance. You can bound the time required by specifying limit, which says not to search before limit. In this case, the match that is found must begin at or after limit.
If greedy is non-
nil, this function extends the match backwards as far as possible, stopping when a single additional previous character cannot be part of a match for regexp. When the match is extended, its starting position is allowed to occur before limit.---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-back "read \"" 3) ⇒ t (looking-back "read \"" 4) ⇒ nil
This predicate function works like
looking-at, but without updating the match data.
If this variable is non-
nil, it should be a regular expression that says how to search for whitespace. In that case, any group of spaces in a regular expression being searched for stands for use of this regular expression. However, spaces inside of constructs such as ‘[...]’ and ‘*’, ‘+’, ‘?’ are not affected bysearch-spaces-regexp.Since this variable affects all regular expression search and match constructs, you should bind it temporarily for as small as possible a part of the code.
The usual regular expression functions do backtracking when necessary to handle the ‘\|’ and repetition constructs, but they continue this only until they find some match. Then they succeed and report the first match found.
This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match.
The POSIX search and match functions do not properly support the non-greedy repetition operators (see non-greedy). This is because POSIX backtracking conflicts with the semantics of non-greedy repetition.
This is like
re-search-forwardexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
re-search-backwardexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
looking-atexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
string-matchexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
Emacs keeps track of the start and end positions of the segments of text found during a search; this is called the match data. Thanks to the match data, you can search for a complex pattern, such as a date in a mail message, and then extract parts of the match under control of the pattern.
Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten.
This function replaces all or part of the text matched by the last search. It works by means of the match data.
This function replaces the text in the buffer (or in string) that was matched by the last search. It replaces that text with replacement.
If you did the last search in a buffer, you should specify
nilfor string and make sure that the current buffer when you callreplace-matchis the one in which you did the searching or matching. Thenreplace-matchdoes the replacement by editing the buffer; it leaves point at the end of the replacement text, and returnst.If you did the search in a string, pass the same string as string. Then
replace-matchdoes the replacement by constructing and returning a new string.If fixedcase is non-
nil, thenreplace-matchuses the replacement text without case conversion; otherwise, it converts the replacement text depending upon the capitalization of the text to be replaced. If the original text is all upper case, this converts the replacement text to upper case. If all words of the original text are capitalized, this capitalizes all the words of the replacement text. If all the words are one-letter and they are all upper case, they are treated as capitalized words rather than all-upper-case words.If literal is non-
nil, then replacement is inserted exactly as it is, the only alterations being case changes as needed. If it isnil(the default), then the character ‘\’ is treated specially. If a ‘\’ appears in replacement, then it must be part of one of the following sequences:
- ‘\&’
- ‘\&’ stands for the entire text being replaced.
- ‘\n’
- ‘\n’, where n is a digit, stands for the text that matched the nth subexpression in the original regexp. Subexpressions are those expressions grouped inside ‘\(...\)’. If the nth subexpression never matched, an empty string is substituted.
- ‘\\’
- ‘\\’ stands for a single ‘\’ in the replacement text.
These substitutions occur after case conversion, if any, so the strings they substitute are never case-converted.
If subexp is non-
nil, that says to replace just subexpression number subexp of the regexp that was matched, not the entire match. For example, after matching ‘foo \(ba*r\)’, callingreplace-matchwith 1 as subexp means to replace just the text that matched ‘\(ba*r\)’.
This function returns the text that would be inserted into the buffer by
replace-match, but without modifying the buffer. It is useful if you want to present the user with actual replacement result, with constructs like ‘\n’ or ‘\&’ substituted with matched groups. Arguments replacement and optional fixedcase, literal, string and subexp have the same meaning as forreplace-match.
This section explains how to use the match data to find out what was matched by the last search or match operation, if it succeeded.
You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which. If count is zero, you are asking about the entire match. If count is positive, it specifies which subexpression you want.
Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, ‘\(...\)’. The countth subexpression is found by counting occurrences of ‘\(’ from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions—after a simple string search, the only information available is about the entire match.
Every successful search sets the match data. Therefore, you should query the match data immediately after searching, before calling any other function that might perform another search. Alternatively, you may save and restore the match data (see Saving Match Data) around the call to functions that could perform another search.
A search which fails may or may not alter the match data. In the past, a failing search did not do this, but we may change it in the future. So don't try to rely on the value of the match data after a failing search.
This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if count is zero, or just the portion corresponding to the countth parenthetical subexpression, if count is positive.
If the last such operation was done against a string with
string-match, then you should pass the same string as the argument in-string. After a buffer search or match, you should omit in-string or passnilfor it; but you should make sure that the current buffer when you callmatch-stringis the one in which you did the searching or matching.The value is
nilif count is out of range, or for a subexpression inside a ‘\|’ alternative that wasn't used or a repetition that repeated zero times.
This function is like
match-stringexcept that the result has no text properties.
This function returns the position of the start of text matched by the last regular expression searched for, or a subexpression of it.
If count is zero, then the value is the position of the start of the entire match. Otherwise, count specifies a subexpression in the regular expression, and the value of the function is the starting position of the match for that subexpression.
The value is
nilfor a subexpression inside a ‘\|’ alternative that wasn't used or a repetition that repeated zero times.
This function is like
match-beginningexcept that it returns the position of the end of the match, rather than the position of the beginning.
Here is an example of using the match data, with a comment showing the positions within the text:
(string-match "\\(qu\\)\\(ick\\)"
"The quick fox jumped quickly.")
;0123456789
⇒ 4
(match-string 0 "The quick fox jumped quickly.")
⇒ "quick"
(match-string 1 "The quick fox jumped quickly.")
⇒ "qu"
(match-string 2 "The quick fox jumped quickly.")
⇒ "ick"
(match-beginning 1) ; The beginning of the match
⇒ 4 ; with ‘qu’ is at index 4.
(match-beginning 2) ; The beginning of the match
⇒ 6 ; with ‘ick’ is at index 6.
(match-end 1) ; The end of the match
⇒ 6 ; with ‘qu’ is at index 6.
(match-end 2) ; The end of the match
⇒ 9 ; with ‘ick’ is at index 9.
Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word ‘in’. The beginning of the entire match is at the 9th character of the buffer (‘T’), and the beginning of the match for the first subexpression is at the 13th character (‘c’).
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
⇒ (17 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(In this case, the index returned is a buffer position; the first character of the buffer counts as 1.)
The functions match-data and set-match-data read or
write the entire match data, all at once.
This function returns a list of positions (markers or integers) that record all the information on what text the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element number 2n corresponds to
(match-beginningn); and element number 2n + 1 corresponds to(match-endn).Normally all the elements are markers or
nil, but if integers is non-nil, that means to use integers instead of markers. (In that case, the buffer itself is appended as an additional element at the end of the list, to facilitate complete restoration of the match data.) If the last match was done on a string withstring-match, then integers are always used, since markers can't point into a string.If reuse is non-
nil, it should be a list. In that case,match-datastores the match data in reuse. That is, reuse is destructively modified. reuse does not need to have the right length. If it is not long enough to contain the match data, it is extended. If it is too long, the length of reuse stays the same, but the elements that were not used are set tonil. The purpose of this feature is to reduce the need for garbage collection.If reseat is non-
nil, all markers on the reuse list are reseated to point to nowhere.As always, there must be no possibility of intervening searches between the call to a search function and the call to
match-datathat is intended to access the match data for that search.(match-data) ⇒ (#<marker at 9 in foo> #<marker at 17 in foo> #<marker at 13 in foo> #<marker at 17 in foo>)
This function sets the match data from the elements of match-list, which should be a list that was the value of a previous call to
match-data. (More precisely, anything that has the same format will work.)If match-list refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way.
If reseat is non-
nil, all markers on the match-list list are reseated to point to nowhere.
store-match-datais a semi-obsolete alias forset-match-data.
When you call a function that may do a search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data:
(re-search-forward "The \\(cat \\)")
⇒ 48
(foo) ; Perhaps foo does
; more searching.
(match-end 0)
⇒ 61 ; Unexpected result---not 48!
You can save and restore the match data with save-match-data:
This macro executes body, saving and restoring the match data around it. The return value is the value of the last form in body.
You could use set-match-data together with match-data to
imitate the effect of the special form save-match-data. Here is
how:
(let ((data (match-data)))
(unwind-protect
... ; Ok to change the original match data.
(set-match-data data)))
Emacs automatically saves and restores the match data when it runs process filter functions (see Filter Functions) and process sentinels (see Sentinels).
If you want to find all matches for a regexp in part of the buffer,
and replace them, the best way is to write an explicit loop using
re-search-forward and replace-match, like this:
(while (re-search-forward "foo[ \t]+bar" nil t)
(replace-match "foobar"))
See Replacing the Text that Matched, for a
description of replace-match.
However, replacing matches in a string is more complex, especially if you want to do it efficiently. So Emacs provides a function to do this.
This function copies string and searches it for matches for regexp, and replaces them with rep. It returns the modified copy. If start is non-
nil, the search for matches starts at that index in string, so matches starting before that index are not changed.This function uses
replace-matchto do the replacement, and it passes the optional arguments fixedcase, literal and subexp along toreplace-match.Instead of a string, rep can be a function. In that case,
replace-regexp-in-stringcalls rep for each match, passing the text of the match as its sole argument. It collects the value rep returns and passes that toreplace-matchas the replacement string. The match-data at this point are the result of matching regexp against a substring of string.
If you want to write a command along the lines of query-replace,
you can use perform-replace to do the work.
This function is the guts of
query-replaceand related commands. It searches for occurrences of from-string in the text between positions start and end and replaces some or all of them. If start isnil(or omitted), point is used instead, and the end of the buffer's accessible portion is used for end.If query-flag is
nil, it replaces all occurrences; otherwise, it asks the user what to do about each one.If regexp-flag is non-
nil, then from-string is considered a regular expression; otherwise, it must match literally. If delimited-flag is non-nil, then only replacements surrounded by word boundaries are considered.The argument replacements specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order.
If replacements is a cons cell,
(function.data), this means to call function after each match to get the replacement text. This function is called with two arguments: data, and the number of replacements already made.If repeat-count is non-
nil, it should be an integer. Then it specifies how many times to use each of the strings in the replacements list before advancing cyclically to the next one.If from-string contains upper-case letters, then
perform-replacebindscase-fold-searchtonil, and it uses thereplacementswithout altering the case of them.Normally, the keymap
query-replace-mapdefines the possible user responses for queries. The argument map, if non-nil, specifies a keymap to use instead ofquery-replace-map.This function uses one of two functions to search for the next occurrence of from-string. These functions are specified by the values of two variables:
replace-re-search-functionandreplace-search-function. The former is called when the argument regexp-flag is non-nil, the latter when it isnil.
This variable holds a special keymap that defines the valid user responses for
perform-replaceand the commands that use it, as well asy-or-n-pandmap-y-or-n-p. This map is unusual in two ways:
- The “key bindings” are not commands, just symbols that are meaningful to the functions that use this map.
- Prefix keys are not supported; each key binding must be for a single-event key sequence. This is because the functions don't use
read-key-sequenceto get the input; instead, they read a single event and look it up “by hand.”
Here are the meaningful “bindings” for query-replace-map.
Several of them are meaningful only for query-replace and
friends.
actskipexitact-and-exitact-and-showautomaticbackupeditdelete-and-editrecenterquity-or-n-p and related functions
use this answer.
helpThis variable holds a keymap that extends
query-replace-mapby providing additional keybindings that are useful in multi-buffer replacements.
This variable specifies a function that
perform-replacecalls to search for the next string to replace. Its default value issearch-forward. Any other value should name a function of 3 arguments: the first 3 arguments ofsearch-forward(see String Search).
This variable specifies a function that
perform-replacecalls to search for the next regexp to replace. Its default value isre-search-forward. Any other value should name a function of 3 arguments: the first 3 arguments ofre-search-forward(see Regexp Search).
This section describes some variables that hold regular expressions used for certain purposes in editing:
This is the regular expression describing line-beginnings that separate pages. The default value is
"^\014"(i.e.,"^^L"or"^\C-l"); this matches a line that starts with a formfeed character.
The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use ‘^’ to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that ‘^’ would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a ‘^’ would be incorrect. However, a ‘^’ is harmless in modes where a left margin is never used.
This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change
paragraph-startalso.) The default value is"[ \t\f]*$", which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin).
This is the regular expression for recognizing the beginning of a line that starts or separates paragraphs. The default value is
"\f\\|[ \t]*$", which matches a line containing only whitespace or starting with a form feed (after its left margin).
If non-
nil, the value should be a regular expression describing the end of a sentence, including the whitespace following the sentence. (All paragraph boundaries also end sentences, regardless.)If the value is
nil, the default, then the functionsentence-endhas to construct the regexp. That is why you should always call the functionsentence-endto obtain the regexp to be used to recognize the end of a sentence.
This function returns the value of the variable
sentence-end, if non-nil. Otherwise it returns a default value based on the values of the variablessentence-end-double-space(see Definition of sentence-end-double-space),sentence-end-without-periodandsentence-end-without-space.
A syntax table specifies the syntactic textual function of each character. This information is used by the parsing functions, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see Word Motion) and the list motion functions (see List Motion), as well as the functions in this chapter.
A syntax table provides Emacs with the information that determines the syntactic use of each character in a buffer. This information is used by the parsing commands, the complex movement commands, and others to determine where words, symbols, and other syntactic constructs begin and end. The current syntax table controls the meaning of the word motion functions (see Word Motion) and the list motion functions (see List Motion) as well as the functions in this chapter.
A syntax table is a char-table (see Char-Tables). The element at index c describes the character with code c. The element's value should be a list that encodes the syntax of the character in question.
Syntax tables are used only for moving across text, not for the Emacs Lisp reader. Emacs Lisp uses built-in syntactic rules when reading Lisp expressions, and these rules cannot be changed. (Some Lisp systems provide ways to redefine the read syntax, but we decided to leave this feature out of Emacs Lisp for simplicity.)
Each buffer has its own major mode, and each major mode has its own idea of the syntactic class of various characters. For example, in Lisp mode, the character ‘;’ begins a comment, but in C mode, it terminates a statement. To support these variations, Emacs makes the choice of syntax table local to each buffer. Typically, each major mode has its own syntax table and installs that table in each buffer that uses that mode. Changing this table alters the syntax in all those buffers as well as in any buffers subsequently put in that mode. Occasionally several similar modes share one syntax table. See Example Major Modes, for an example of how to set up a syntax table.
A syntax table can inherit the data for some characters from the standard syntax table, while specifying other characters itself. The “inherit” syntax class means “inherit this character's syntax from the standard syntax table.” Just changing the standard syntax for a character affects all syntax tables that inherit from it.
This section describes the syntax classes and flags that denote the
syntax of a character, and how they are represented as a syntax
descriptor, which is a Lisp string that you pass to
modify-syntax-entry to specify the syntax you want.
The syntax table specifies a syntax class for each character. There is no necessary relationship between the class of a character in one syntax table and its class in any other table.
Each class is designated by a mnemonic character, which serves as the name of the class when you need to specify a class. Usually the designator character is one that is often assigned that class; however, its meaning as a designator is unvarying and independent of what syntax that character currently has. Thus, ‘\’ as a designator character always gives “escape character” syntax, regardless of what syntax ‘\’ currently has.
A syntax descriptor is a Lisp string that specifies a syntax class, a matching character (used only for the parenthesis classes) and flags. The first character is the designator for a syntax class. The second character is the character to match; if it is unused, put a space there. Then come the characters for any desired flags. If no matching character or flags are needed, one character is sufficient.
For example, the syntax descriptor for the character ‘*’ in C mode is ‘. 23’ (i.e., punctuation, matching character slot unused, second character of a comment-starter, first character of a comment-ender), and the entry for ‘/’ is ‘. 14’ (i.e., punctuation, matching character slot unused, first character of a comment-starter, second character of a comment-ender).
Here is a table of syntax classes, the characters that stand for them, their meanings, and examples of their use.
Whitespace characters (designated by ‘ ’ or ‘-’) separate symbols and words from each other. Typically, whitespace characters have no other syntactic significance, and multiple whitespace characters are syntactically equivalent to a single one. Space, tab, newline and formfeed are classified as whitespace in almost all major modes.
Word constituents (designated by ‘w’) are parts of words in human languages, and are typically used in variable and command names in programs. All upper- and lower-case letters, and the digits, are typically word constituents.
Symbol constituents (designated by ‘_’) are the extra characters that are used in variable and command names along with word constituents. For example, the symbol constituents class is used in Lisp mode to indicate that certain characters may be part of symbol names even though they are not part of English words. These characters are ‘$&*+-_<>’. In standard C, the only non-word-constituent character that is valid in symbols is underscore (‘_’).
Punctuation characters (designated by ‘.’) are those characters that are used as punctuation in English, or are used in some way in a programming language to separate symbols from one another. Some programming language modes, such as Emacs Lisp mode, have no characters in this class since the few characters that are not symbol or word constituents all have other uses. Other programming language modes, such as C mode, use punctuation syntax for operators.
Open and close parenthesis characters are characters used in dissimilar pairs to surround sentences or expressions. Such a grouping is begun with an open parenthesis character and terminated with a close. Each open parenthesis character matches a particular close parenthesis character, and vice versa. Normally, Emacs indicates momentarily the matching open parenthesis when you insert a close parenthesis. See Blinking.
The class of open parentheses is designated by ‘(’, and that of close parentheses by ‘)’.
In English text, and in C code, the parenthesis pairs are ‘()’, ‘[]’, and ‘{}’. In Emacs Lisp, the delimiters for lists and vectors (‘()’ and ‘[]’) are classified as parenthesis characters.
String quote characters (designated by ‘"’) are used in many languages, including Lisp and C, to delimit string constants. The same string quote character appears at the beginning and the end of a string. Such quoted strings do not nest.
The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed.
The Lisp modes have two string quote characters: double-quote (‘"’) and vertical bar (‘|’). ‘|’ is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and single-quote (‘'’) for character constants.
English text has no string quote characters because English is not a programming language. Although quotation marks are used in English, we do not want them to turn off the usual syntactic properties of other characters in the quotation.
An escape character (designated by ‘\’) starts an escape sequence such as is used in C string and character constants. The character ‘\’ belongs to this class in both C and Lisp. (In C, it is used thus only inside strings, but it turns out to cause no trouble to treat it this way throughout C code.)
Characters in this class count as part of words if
words-include-escapesis non-nil. See Word Motion.
A character quote character (designated by ‘/’) quotes the following character so that it loses its normal syntactic meaning. This differs from an escape character in that only the character immediately following is ever affected.
Characters in this class count as part of words if
words-include-escapesis non-nil. See Word Motion.This class is used for backslash in TeX mode.
Paired delimiter characters (designated by ‘$’) are like string quote characters except that the syntactic properties of the characters between the delimiters are not suppressed. Only TeX mode uses a paired delimiter presently—the ‘$’ that both enters and leaves math mode.
An expression prefix operator (designated by ‘'’) is used for syntactic operators that are considered as part of an expression if they appear next to one. In Lisp modes, these characters include the apostrophe, ‘'’ (used for quoting), the comma, ‘,’ (used in macros), and ‘#’ (used in the read syntax for certain data types).
The comment starter and comment ender characters are used in various languages to delimit comments. These classes are designated by ‘<’ and ‘>’, respectively.
English text has no comment characters. In Lisp, the semicolon (‘;’) starts a comment and a newline or formfeed ends one.
This syntax class does not specify a particular syntax. It says to look in the standard syntax table to find the syntax of this character. The designator for this syntax class is ‘@’.
A generic comment delimiter (designated by ‘!’) starts or ends a special kind of comment. Any generic comment delimiter matches any generic comment delimiter, but they cannot match a comment starter or comment ender; generic comment delimiters can only match each other.
This syntax class is primarily meant for use with the
syntax-tabletext property (see Syntax Properties). You can mark any range of characters as forming a comment, by giving the first and last characters of the rangesyntax-tableproperties identifying them as generic comment delimiters.
A generic string delimiter (designated by ‘|’) starts or ends a string. This class differs from the string quote class in that any generic string delimiter can match any other generic string delimiter; but they do not match ordinary string quote characters.
This syntax class is primarily meant for use with the
syntax-tabletext property (see Syntax Properties). You can mark any range of characters as forming a string constant, by giving the first and last characters of the rangesyntax-tableproperties identifying them as generic string delimiters.
In addition to the classes, entries for characters in a syntax table can specify flags. There are seven possible flags, represented by the characters ‘1’, ‘2’, ‘3’, ‘4’, ‘b’, ‘n’, and ‘p’.
All the flags except ‘n’ and ‘p’ are used to describe multi-character comment delimiters. The digit flags indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as ‘*’ in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (‘/*’), and the first character of an end-of-comment sequence (‘*/’).
Here is a table of the possible flags for a character c, and what they mean:
Emacs supports two comment styles simultaneously in any one syntax table. This is for the sake of C++. Each style of comment syntax has its own comment-start sequence and its own comment-end sequence. Each comment must stick to one style or the other; thus, if it starts with the comment-start sequence of style “b,” it must also end with the comment-end sequence of style “b.”
The two comment-start sequences must begin with the same character; only the second character may differ. Mark the second character of the “b”-style comment-start sequence with the ‘b’ flag.
A comment-end sequence (one or two characters) applies to the “b” style if its first character has the ‘b’ flag set; otherwise, it applies to the “a” style.
The appropriate comment syntax settings for C++ are as follows:
This defines four comment-delimiting sequences:
The function backward-prefix-chars moves back over these
characters, as well as over characters whose primary syntax class is
prefix (‘'’). See Motion and Syntax.
In this section we describe functions for creating, accessing and altering syntax tables.
This function creates a new syntax table, with all values initialized to
nil. If table is non-nil, it becomes the parent of the new syntax table, otherwise the standard syntax table is the parent. Like all char-tables, a syntax table inherits from its parent. Thus the original syntax of all characters in the returned syntax table is determined by the parent. See Char-Tables.Most major mode syntax tables are created in this way.
This function constructs a copy of table and returns it. If table is not supplied (or is
nil), it returns a copy of the standard syntax table. Otherwise, an error is signaled if table is not a syntax table.
This function sets the syntax entry for char according to syntax-descriptor. char can be a character, or a cons cell of the form
(min.max); in the latter case, the function sets the syntax entries for all characters in the range between min and max, inclusive.The syntax is changed only for table, which defaults to the current buffer's syntax table, and not in any other syntax table. The argument syntax-descriptor specifies the desired syntax; this is a string beginning with a class designator character, and optionally containing a matching character and flags as well. See Syntax Descriptors.
This function always returns
nil. The old syntax information in the table for this character is discarded.An error is signaled if the first character of the syntax descriptor is not one of the seventeen syntax class designator characters. An error is also signaled if char is not a character.
Examples:
;; Put the space character in class whitespace. (modify-syntax-entry ?\s " ") ⇒ nil ;; Make ‘$’ an open parenthesis character, ;; with ‘^’ as its matching close. (modify-syntax-entry ?$ "(^") ⇒ nil ;; Make ‘^’ a close parenthesis character, ;; with ‘$’ as its matching open. (modify-syntax-entry ?^ ")$") ⇒ nil ;; Make ‘/’ a punctuation character, ;; the first character of a start-comment sequence, ;; and the second character of an end-comment sequence. ;; This is used in C mode. (modify-syntax-entry ?/ ". 14") ⇒ nil
This function returns the syntax class of character, represented by its mnemonic designator character. This returns only the class, not any matching parenthesis or flags.
An error is signaled if char is not a character.
The following examples apply to C mode. The first example shows that the syntax class of space is whitespace (represented by a space). The second example shows that the syntax of ‘/’ is punctuation. This does not show the fact that it is also part of comment-start and -end sequences. The third example shows that open parenthesis is in the class of open parentheses. This does not show the fact that it has a matching character, ‘)’.
(string (char-syntax ?\s)) ⇒ " " (string (char-syntax ?/)) ⇒ "." (string (char-syntax ?\()) ⇒ "("We use
stringto make it easier to see the character returned bychar-syntax.
This function makes table the syntax table for the current buffer. It returns table.
This function returns the current syntax table, which is the table for the current buffer.
This macro executes body using table as the current syntax table. It returns the value of the last form in body, after restoring the old current syntax table.
Since each buffer has its own current syntax table, we should make that more precise:
with-syntax-tabletemporarily alters the current syntax table of whichever buffer is current at the time the macro execution starts. Other buffers are not affected.
When the syntax table is not flexible enough to specify the syntax of
a language, you can use syntax-table text properties to
override the syntax table for specific character occurrences in the
buffer. See Text Properties. You can use Font Lock mode to set
syntax-table text properties. See Setting Syntax Properties.
The valid values of syntax-table text property are:
(syntax-code . matching-char)nilnil, the character's syntax is determined from
the current syntax table in the usual way.
If this is non-
nil, the syntax scanning functions pay attention to syntax text properties. Otherwise they use only the current syntax table.
This section describes functions for moving across characters that have certain syntax classes.
This function moves point forward across characters having syntax classes mentioned in syntaxes (a string of syntax class characters). It stops when it encounters the end of the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with ‘^’, then the function skips characters whose syntax is not in syntaxes.
The return value is the distance traveled, which is a nonnegative integer.
This function moves point backward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the beginning of the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with ‘^’, then the function skips characters whose syntax is not in syntaxes.
The return value indicates the distance traveled. It is an integer that is zero or less.
This function moves point backward over any number of characters with expression prefix syntax. This includes both characters in the expression prefix syntax class, and characters with the ‘p’ flag.
This section describes functions for parsing and scanning balanced expressions, also known as sexps. Basically, a sexp is either a balanced parenthetical grouping, a string, or a symbol name (a sequence of characters whose syntax is either word constituent or symbol constituent). However, characters whose syntax is expression prefix are treated as part of the sexp if they appear next to it.
The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See List Motion, for convenient higher-level functions for moving over balanced expressions.
A character's syntax controls how it changes the state of the parser, rather than describing the state itself. For example, a string delimiter character toggles the parser state between “in-string” and “in-code,” but the syntax of characters does not directly say whether they are inside a string. For example (note that 15 is the syntax code for generic string delimiters),
(put-text-property 1 9 'syntax-table '(15 . nil))
does not tell Emacs that the first eight chars of the current buffer are a string, but rather that they are all string delimiters. As a result, Emacs treats them as four consecutive empty string constants.
This section describes simple point-motion functions that operate based on parsing expressions.
This function scans forward count balanced parenthetical groupings from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.
If depth is nonzero, parenthesis depth counting begins from that value. The only candidates for stopping are places where the depth in parentheses becomes zero;
scan-listscounts count such places and then stops. Thus, a positive value for depth means go out depth levels of parenthesis.Scanning ignores comments if
parse-sexp-ignore-commentsis non-nil.If the scan reaches the beginning or end of the buffer (or its accessible portion), and the depth is not zero, an error is signaled. If the depth is zero but the count is not used up,
nilis returned.
This function scans forward count sexps from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.
Scanning ignores comments if
parse-sexp-ignore-commentsis non-nil.If the scan reaches the beginning or end of (the accessible part of) the buffer while in the middle of a parenthetical grouping, an error is signaled. If it reaches the beginning or end between groupings but before count is used up,
nilis returned.
This function moves point forward across count complete comments (that is, including the starting delimiter and the terminating delimiter if any), plus any whitespace encountered on the way. It moves backward if count is negative. If it encounters anything other than a comment or whitespace, it stops, leaving point at the place where it stopped. This includes (for instance) finding the end of a comment when moving forward and expecting the beginning of one. The function also stops immediately after moving over the specified number of complete comments. If count comments are found as expected, with nothing except whitespace between them, it returns
t; otherwise it returnsnil.This function cannot tell whether the “comments” it traverses are embedded within a string. If they look like comments, it treats them as comments.
To move forward over all comments and whitespace following point, use
(forward-comment (buffer-size)). (buffer-size) is a good
argument to use, because the number of comments in the buffer cannot
exceed that many.
For syntactic analysis, such as in indentation, often the useful thing is to compute the syntactic state corresponding to a given buffer position. This function does that conveniently.
This function returns the parser state (see next section) that the parser would reach at position pos starting from the beginning of the buffer. This is equivalent to
(parse-partial-sexp (point-min)pos), except thatsyntax-ppssuses a cache to speed up the computation. Due to this optimization, the 2nd value (previous complete subexpression) and 6th value (minimum parenthesis depth) of the returned parser state are not meaningful.
syntax-ppss automatically hooks itself to
before-change-functions to keep its cache consistent. But
updating can fail if syntax-ppss is called while
before-change-functions is temporarily let-bound, or if the
buffer is modified without obeying the hook, such as when using
inhibit-modification-hooks. For this reason, it is sometimes
necessary to flush the cache manually.
This function flushes the cache used by
syntax-ppss, starting at position beg. The remaining arguments, ignored-args, are ignored; this function accepts them so that it can be directly used on hooks such asbefore-change-functions(see Change Hooks).
Major modes can make syntax-ppss run faster by specifying
where it needs to start parsing.
If this is non-
nil, it should be a function that moves to an earlier buffer position where the parser state is equivalent tonil—in other words, a position outside of any comment, string, or parenthesis.syntax-ppssuses it to further optimize its computations, when the cache gives no help.
A parser state is a list of ten elements describing the final state of parsing text syntactically as part of an expression. The parsing functions in the following sections return a parser state as the value, and in some cases accept one as an argument also, so that you can resume parsing after it stops. Here are the meanings of the elements of the parser state:
nil if none.
nil if none.
nil if inside a string. More precisely, this is the
character that will terminate the string, or t if a generic
string delimiter character should terminate it.
t if inside a comment (of either style),
or the comment nesting level if inside a kind of comment
that can be nested.
t if point is just after a quote character.
nil for a comment of style
“a” or when not inside a comment, t for a comment of style
“b,” and syntax-table for a comment that should be ended by a
generic comment delimiter character.
nil.
Elements 1, 2, and 6 are ignored in a state which you pass as an argument to continue parsing, and elements 8 and 9 are used only in trivial cases. Those elements serve primarily to convey information to the Lisp program which does the parsing.
One additional piece of useful information is available from a parser state using this function:
This function extracts, from parser state state, the last position scanned in the parse which was at top level in grammatical structure. “At top level” means outside of any parentheses, comments, or strings.
The value is
nilif state represents a parse which has arrived at a top level position.
We have provided this access function rather than document how the data is represented in the state, because we plan to change the representation in the future.
The most basic way to use the expression parser is to tell it to start at a given position with a certain state, and parse up to a specified end position.
This function parses a sexp in the current buffer starting at start, not scanning past limit. It stops at position limit or when certain criteria described below are met, and sets point to the location where parsing stops. It returns a parser state describing the status of the parse at the point where it stops.
If the third argument target-depth is non-
nil, parsing stops if the depth in parentheses becomes equal to target-depth. The depth starts at 0, or at whatever is given in state.If the fourth argument stop-before is non-
nil, parsing stops when it comes to any character that starts a sexp. If stop-comment is non-nil, parsing stops when it comes to the start of a comment. If stop-comment is the symbolsyntax-table, parsing stops after the start of a comment or a string, or the end of a comment or a string, whichever comes first.If state is
nil, start is assumed to be at the top level of parenthesis structure, such as the beginning of a function definition. Alternatively, you might wish to resume parsing in the middle of the structure. To do this, you must provide a state argument that describes the initial status of parsing. The value returned by a previous call toparse-partial-sexpwill do nicely.
If this variable is non-
nil,scan-sexpstreats all non-ASCII characters as symbol constituents regardless of what the syntax table says about them. (However, text properties can still override the syntax.)
If the value is non-
nil, then comments are treated as whitespace by the functions in this section and byforward-sexp,scan-listsandscan-sexps.
The behavior of parse-partial-sexp is also affected by
parse-sexp-lookup-properties (see Syntax Properties).
You can use forward-comment to move forward or backward over
one comment or several comments.
Most of the major modes in Emacs have their own syntax tables. Here are several of them:
This function returns the standard syntax table, which is the syntax table used in Fundamental mode.
The value of this variable is the syntax table used in Text mode.
The value of this variable is the syntax table used in Emacs Lisp mode by editing commands. (It has no effect on the Lisp
readfunction.)
Lisp programs don't usually work with the elements directly; the Lisp-level syntax table functions usually work with syntax descriptors (see Syntax Descriptors). Nonetheless, here we document the internal format. This format is used mostly when manipulating syntax properties.
Each element of a syntax table is a cons cell of the form
(syntax-code . matching-char). The car,
syntax-code, is an integer that encodes the syntax class, and any
flags. The cdr, matching-char, is non-nil if
a character to match was specified.
This table gives the value of syntax-code which corresponds to each syntactic type.
| Integer Class | Integer Class |
Integer Class
| |
| 0 whitespace | 5 close parenthesis |
10 character quote
| |
| 1 punctuation | 6 expression prefix |
11 comment-start
| |
| 2 word | 7 string quote |
12 comment-end
| |
| 3 symbol | 8 paired delimiter |
13 inherit
| |
| 4 open parenthesis | 9 escape |
14 generic comment
| |
|
15 generic string
|
For example, the usual syntax value for ‘(’ is (4 . 41).
(41 is the character code for ‘)’.)
The flags are encoded in higher order bits, starting 16 bits from the least significant bit. This table gives the power of two which corresponds to each syntax flag.
| Prefix Flag | Prefix Flag |
Prefix Flag
| |
‘1’ (lsh 1 16)
|
‘4’ (lsh 1 19)
|
‘b’ (lsh 1 21)
| |
‘2’ (lsh 1 17)
|
‘p’ (lsh 1 20)
|
‘n’ (lsh 1 22)
| |
‘3’ (lsh 1 18)
|
This function returns the internal form corresponding to the syntax descriptor desc, a cons cell
(syntax-code.matching-char).
This function returns the syntax code of the character in the buffer after position pos, taking account of syntax properties as well as the syntax table. If pos is outside the buffer's accessible portion (see accessible portion), this function returns
nil.
This function returns the syntax class of the syntax code syntax. (It masks off the high 16 bits that hold the flags encoded in the syntax descriptor.) If syntax is
nil, it returnsnil; this is so evaluating the expression(syntax-class (syntax-after pos))where
posis outside the buffer's accessible portion, will yieldnilwithout throwing errors or producing wrong syntax class codes.
Categories provide an alternate way of classifying characters syntactically. You can define several categories as needed, then independently assign each character to one or more categories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one character to belong to several categories.
Each buffer has a category table which records which categories are defined and also which characters belong to each category. Each category table defines its own categories, but normally these are initialized by copying from the standard categories table, so that the standard categories are available in all modes.
Each category has a name, which is an ASCII printing character in
the range ‘ ’ to ‘~’. You specify the name of a category
when you define it with define-category.
The category table is actually a char-table (see Char-Tables).
The element of the category table at index c is a category
set—a bool-vector—that indicates which categories character c
belongs to. In this category set, if the element at index cat is
t, that means category cat is a member of the set, and that
character c belongs to category cat.
For the next three functions, the optional argument table defaults to the current buffer's category table.
This function defines a new category, with name char and documentation docstring, for the category table table.
This function returns the documentation string of category category in category table table.
(category-docstring ?a) ⇒ "ASCII" (category-docstring ?l) ⇒ "Latin"
This function returns a category name (a character) which is not currently defined in table. If all possible categories are in use in table, it returns
nil.
This function returns
tif object is a category table, otherwisenil.
This function constructs a copy of table and returns it. If table is not supplied (or is
nil), it returns a copy of the standard category table. Otherwise, an error is signaled if table is not a category table.
This function makes table the category table for the current buffer. It returns table.
This creates and returns an empty category table. In an empty category table, no categories have been allocated, and no characters belong to any categories.
This function returns a new category set—a bool-vector—whose initial contents are the categories listed in the string categories. The elements of categories should be category names; the new category set has
tfor each of those categories, andnilfor all other categories.(make-category-set "al") ⇒ #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function returns the category set for character char in the current buffer's category table. This is the bool-vector which records which categories the character char belongs to. The function
char-category-setdoes not allocate storage, because it returns the same bool-vector that exists in the category table.(char-category-set ?a) ⇒ #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function converts the category set category-set into a string containing the characters that designate the categories that are members of the set.
(category-set-mnemonics (char-category-set ?a)) ⇒ "al"
This function modifies the category set of char in category table table (which defaults to the current buffer's category table). char can be a character, or a cons cell of the form
(min.max); in the latter case, the function modifies the category sets of all characters in the range between min and max, inclusive.Normally, it modifies a category set by adding category to it. But if reset is non-
nil, then it deletes category instead.
This function describes the category specifications in the current category table. It inserts the descriptions in a buffer, and then displays that buffer. If buffer-or-name is non-
nil, it describes the category table of that buffer instead.
An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.
The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.
An abbrev table is represented as an obarray. See Creating Symbols, for information about obarrays. Each abbreviation is represented by a symbol in the obarray. The symbol's name is the abbreviation; its value is the expansion; its function definition is the hook function for performing the expansion (see Defining Abbrevs); and its property list cell contains various additional properties, including the use count and the number of times the abbreviation has been expanded (see Abbrev Properties).
Certain abbrevs, called system abbrevs, are defined by a major
mode instead of the user. A system abbrev is identified by its
non-nil :system property (see Abbrev Properties).
When abbrevs are saved to an abbrev file, system abbrevs are omitted.
See Abbrev Files.
Because the symbols used for abbrevs are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in an extremely nonstandard way.
For the user-level commands for abbrevs, see Abbrev Mode.
Abbrev mode is a minor mode controlled by the variable
abbrev-mode.
If this variable is non-
nil, abbrevs are automatically expanded in the buffer. If the value isnil, abbrevs may be defined, but they are not expanded automatically.This variable automatically becomes buffer-local when set in any fashion.
This section describes how to create and manipulate abbrev tables.
This function creates and returns a new, empty abbrev table—an obarray containing no symbols. It is a vector filled with zeros. props is a property list that is applied to the new table (see Abbrev Table Properties).
This function returns a non-
nilvalue if object is an abbrev table.
This function undefines all the abbrevs in abbrev-table, leaving it empty. It always returns
nil.
This function returns a copy of abbrev-table—a new abbrev table containing the same abbrev definitions. There is one difference between the contents of abbrev-table and the returned copy: all abbrevs in the latter have their property lists set to
nil.
This function defines tabname (a symbol) as an abbrev table name, i.e., as a variable whose value is an abbrev table. It defines abbrevs in the table according to definitions, a list of elements of the form
(abbrevname expansion[hook] [props...]). These elements are passed as arguments todefine-abbrev. The return value is alwaysnil.The optional string docstring is the documentation string of the variable tabname. The property list props is applied to the abbrev table (see Abbrev Table Properties).
If this function is called more than once for the same tabname, subsequent calls add the definitions in definitions to tabname, rather than overriding the entire original contents. (A subsequent call only overrides abbrevs explicitly redefined or undefined in definitions.)
This is a list of symbols whose values are abbrev tables.
define-abbrev-tableadds the new abbrev table name to this list.
This function inserts before point a description of the abbrev table named name. The argument name is a symbol whose value is an abbrev table. The return value is always
nil.If human is non-
nil, the description is human-oriented. System abbrevs are listed and identified as such. Otherwise the description is a Lisp expression—a call todefine-abbrev-tablethat would define name as it is currently defined, but without the system abbrevs. (The mode or package using name is supposed to add these to name separately.)
define-abbrev is the low-level basic function for defining an
abbrev in an abbrev table.
When a major mode defines a system abbrev, it should call
define-abbrev and specify a t for the :system
property. Be aware that any saved non-“system” abbrevs are restored
at startup, i.e. before some major modes are loaded. Therefore, major
modes should not assume that their abbrev tables are empty when they
are first loaded.
This function defines an abbrev named name, in abbrev-table, to expand to expansion and call hook, with properties props (see Abbrev Properties). The return value is name. The
:systemproperty in props is treated specially here: if it has the valueforce, then it will overwrite an existing definition even for a non-“system” abbrev of the same name.name should be a string. The argument expansion is normally the desired expansion (a string), or
nilto undefine the abbrev. If it is anything but a string ornil, then the abbreviation “expands” solely by running hook.The argument hook is a function or
nil. If hook is non-nil, then it is called with no arguments after the abbrev is replaced with expansion; point is located at the end of expansion when hook is called.If hook is a non-
nilsymbol whoseno-self-insertproperty is non-nil, hook can explicitly control whether to insert the self-inserting input character that triggered the expansion. If hook returns non-nilin this case, that inhibits insertion of the character. By contrast, if hook returnsnil,expand-abbrevalso returnsnil, as if expansion had not really occurred.Normally,
define-abbrevsets the variableabbrevs-changedtot, if it actually changes the abbrev. (This is so that some commands will offer to save the abbrevs.) It does not do this for a system abbrev, since those aren't saved anyway.
If this variable is non-
nil, it means that the user plans to use global abbrevs only. This tells the commands that define mode-specific abbrevs to define global ones instead. This variable does not alter the behavior of the functions in this section; it is examined by their callers.
A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents. Therefore, you can load the file
with load (see How Programs Do Loading). However, the
function quietly-read-abbrev-file is provided as a more
convenient interface.
User-level facilities such as save-some-buffers can save
abbrevs in a file automatically, under the control of variables
described here.
This function reads abbrev definitions from a file named filename, previously written with
write-abbrev-file. If filename is omitted ornil, the file specified inabbrev-file-nameis used.save-abbrevsis set totso that changes will be saved.This function does not display any messages. It returns
nil.
A non-
nilvalue forsave-abbrevsmeans that Emacs should offer the user to save abbrevs when files are saved. If the value issilently, Emacs saves the abbrevs without asking the user.abbrev-file-namespecifies the file to save the abbrevs in.
This variable is set non-
nilby defining or altering any abbrevs (except system abbrevs). This serves as a flag for various Emacs commands to offer to save your abbrevs.
Save all abbrev definitions (except system abbrevs), for all abbrev tables listed in
abbrev-table-name-list, in the file filename, in the form of a Lisp program that when loaded will define the same abbrevs. If filename isnilor omitted,abbrev-file-nameis used. This function returnsnil.
Abbrevs are usually expanded by certain interactive commands,
including self-insert-command. This section describes the
subroutines used in writing such commands, as well as the variables they
use for communication.
This function returns the symbol representing the abbrev named abbrev. The value returned is
nilif that abbrev is not defined. The optional second argument table is the abbrev table in which to look it up. If table isnil, this function tries first the current buffer's local abbrev table, and second the global abbrev table.
This function returns the string that abbrev would expand into (as defined by the abbrev tables used for the current buffer). If abbrev is not a valid abbrev, the function returns
nil. The optional argument table specifies the abbrev table to use, as inabbrev-symbol.
This command expands the abbrev before point, if any. If point does not follow an abbrev, this command does nothing. The command returns the abbrev symbol if it did expansion,
nilotherwise.If the abbrev symbol has a hook function which is a symbol whose
no-self-insertproperty is non-nil, and if the hook function returnsnilas its value, thenexpand-abbrevreturnsnileven though expansion did occur.
This function inserts the abbrev expansion of
abbrev, replacing the text betweenstartandend. Ifstartis omitted, it defaults to point.name, if non-nil, should be the name by which this abbrev was found (a string); it is used to figure out whether to adjust the capitalization of the expansion. The function returnsabbrevif the abbrev was successfully inserted.
This command marks the current location of point as the beginning of an abbrev. The next call to
expand-abbrevwill use the text from here to point (where it is then) as the abbrev to expand, rather than using the previous word as usual.First, this command expands any abbrev before point, unless arg is non-
nil. (Interactively, arg is the prefix argument.) Then it inserts a hyphen before point, to indicate the start of the next abbrev to be expanded. The actual expansion removes the hyphen.
When this is set non-
nil, an abbrev entered entirely in upper case is expanded using all upper case. Otherwise, an abbrev entered entirely in upper case is expanded by capitalizing each word of the expansion.
The value of this variable is a buffer position (an integer or a marker) for
expand-abbrevto use as the start of the next abbrev to be expanded. The value can also benil, which means to use the word before point instead.abbrev-start-locationis set tonileach timeexpand-abbrevis called. This variable is also set byabbrev-prefix-mark.
The value of this variable is the buffer for which
abbrev-start-locationhas been set. Trying to expand an abbrev in any other buffer clearsabbrev-start-location. This variable is set byabbrev-prefix-mark.
This is the
abbrev-symbolof the most recent abbrev expanded. This information is left byexpand-abbrevfor the sake of theunexpand-abbrevcommand (see Expanding Abbrevs).
This is the location of the most recent abbrev expanded. This contains information left by
expand-abbrevfor the sake of theunexpand-abbrevcommand.
This is the exact expansion text of the most recent abbrev expanded, after case conversion (if any). Its value is
nilif the abbrev has already been unexpanded. This contains information left byexpand-abbrevfor the sake of theunexpand-abbrevcommand.
This is a special hook run around the
expand-abbrevfunction. Each function on this hook is called with a single argument: a function that performs the normal abbrev expansion. The hook function can hence do anything it wants before and after performing the expansion. It can also choose not to call its argument, thus overriding the default behavior; or it may even call it several times. The function should return the abbrev symbol if expansion took place.
The following sample code shows a simple use of
abbrev-expand-functions. It assumes that foo-mode is a
mode for editing certain files in which lines that start with ‘#’
are comments. You want to use Text mode abbrevs for those lines. The
regular local abbrev table, foo-mode-abbrev-table is
appropriate for all other lines. Then you can put the following code
in your .emacs file. See Standard Abbrev Tables, for the
definitions of local-abbrev-table and text-mode-abbrev-table.
(defun foo-mode-abbrev-expand-function (expand)
(if (not (save-excursion (forward-line 0) (eq (char-after) ?#)))
;; Performs normal expansion.
(funcall expand)
;; We're inside a comment: use the text-mode abbrevs.
(let ((local-abbrev-table text-mode-abbrev-table))
(funcall expand))))
(add-hook 'foo-mode-hook
#'(lambda ()
(add-hook 'abbrev-expand-functions
'foo-mode-abbrev-expand-function
nil t)))
Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.
This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table.
The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer. It can also be a list of such tables.
The value of this variable is a list of elements of the form
(mode.abbrev-table)where mode is the name of a variable: if the variable is bound to a non-nilvalue, then the abbrev-table is active, otherwise it is ignored. abbrev-table can also be a list of abbrev tables.
This is the local abbrev table used in Fundamental mode; in other words, it is the local abbrev table in all buffers in Fundamental mode.
This is the local abbrev table used in Lisp mode and Emacs Lisp mode.
Abbrevs have properties, some of which influence the way they work.
You can provide them as arguments to define-abbrev and you can
manipulate them with the following functions:
Return the property prop of abbrev, or
nilif the abbrev has no such property.
The following properties have special meanings:
:countdefine-abbrev.
:systemnil, this property marks the abbrev as a system abbrev.
Such abbrevs are not saved (see Abbrev Files).
:enable-functionnil, this property should be a function of no
arguments which returns nil if the abbrev should not be used
and t otherwise.
:case-fixednil, this property indicates that the case of the
abbrev's name is significant and should only match a text with the
same pattern of capitalization. It also disables the code that
modifies the capitalization of the expansion.
Like abbrevs, abbrev tables have properties, some of which influence
the way they work. You can provide them as arguments to
define-abbrev-table and you can manipulate them with the
functions:
Set the property prop of abbrev table table to value val.
Return the property prop of abbrev table table, or
nilif the abbrev has no such property.
The following properties have special meaning:
:enable-function:enable-function abbrev property except that
it applies to all abbrevs in the table and is used even before trying
to find the abbrev before point so it can dynamically modify the
abbrev table.
:case-fixed:case-fixed abbrev property except that it
applies to all abbrevs in the table.
:regexpnil, this property is a regular expression that
indicates how to extract the name of the abbrev before point before
looking it up in the table. When the regular expression matches
before point, the abbrev name is expected to be in submatch 1.
If this property is nil, expand-function defaults to
"\\<\\(\\w+\\)\\W". This property allows the use of abbrevs
whose name contains characters of non-word syntax.
:parents:abbrev-table-modiffIn the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.
A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a “process.” Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.
This function returns
tif object represents an Emacs subprocess,nilotherwise.
In addition to subprocesses of the current Emacs session, you can also access other processes running on your machine. See System Processes.
There are three primitives that create a new subprocess in which to run
a program. One of them, start-process, creates an asynchronous
process and returns a process object (see Asynchronous Processes).
The other two, call-process and call-process-region,
create a synchronous process and do not return a process object
(see Synchronous Processes).
Synchronous and asynchronous processes are explained in the following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.
In all cases, the function's program argument specifies the
program to be run. An error is signaled if the file is not found or
cannot be executed. If the file name is relative, the variable
exec-path contains a list of directories to search. Emacs
initializes exec-path when it starts up, based on the value of
the environment variable PATH. The standard file name
constructs, ‘~’, ‘.’, and ‘..’, are interpreted as
usual in exec-path, but environment variable substitutions
(‘$HOME’, etc.) are not recognized; use
substitute-in-file-name to perform them (see File Name Expansion). nil in this list refers to
default-directory.
Executing a program can also try adding suffixes to the specified name:
This variable is a list of suffixes (strings) to try adding to the specified program file name. The list should include
""if you want the name to be tried exactly as specified. The default value is system-dependent.
Please note: The argument program contains only the name of the program; it may not contain any command-line arguments. You must use args to provide those.
Each of the subprocess-creating functions has a buffer-or-name
argument which specifies where the standard output from the program will
go. It should be a buffer or a buffer name; if it is a buffer name,
that will create the buffer if it does not already exist. It can also
be nil, which says to discard the output unless a filter function
handles it. (See Filter Functions, and Read and Print.)
Normally, you should avoid having multiple processes send output to the
same buffer because their output would be intermixed randomly.
All three of the subprocess-creating functions have a &rest
argument, args. The args must all be strings, and they are
supplied to program as separate command line arguments. Wildcard
characters and other shell constructs have no special meanings in these
strings, since the strings are passed directly to the specified program.
The subprocess gets its current directory from the value of
default-directory (see File Name Expansion).
The subprocess inherits its environment from Emacs, but you can
specify overrides for it with process-environment. See System Environment.
The value of this variable is a string, the name of a directory that contains programs that come with GNU Emacs, programs intended for Emacs to invoke. The program
movemailis an example of such a program; Rmail uses it to fetch new mail from an inbox.
The value of this variable is a list of directories to search for programs to run in subprocesses. Each element is either the name of a directory (i.e., a string), or
nil, which stands for the default directory (which is the value ofdefault-directory). The value ofexec-pathis used bycall-processandstart-processwhen the program argument is not an absolute file name.
Lisp programs sometimes need to run a shell and give it a command
that contains file names that were specified by the user. These
programs ought to be able to support any valid file name. But the shell
gives special treatment to certain characters, and if these characters
occur in the file name, they will confuse the shell. To handle these
characters, use the function shell-quote-argument:
This function returns a string which represents, in shell syntax, an argument whose actual contents are argument. It should work reliably to concatenate the return value into a shell command and then pass it to a shell for execution.
Precisely what this function does depends on your operating system. The function is designed to work with the syntax of your system's standard shell; if you use an unusual shell, you will need to redefine this function.
;; This example shows the behavior on GNU and Unix systems. (shell-quote-argument "foo > bar") ⇒ "foo\\ \\>\\ bar" ;; This example shows the behavior on MS-DOS and MS-Windows. (shell-quote-argument "foo > bar") ⇒ "\"foo > bar\""Here's an example of using
shell-quote-argumentto construct a shell command:(concat "diff -c " (shell-quote-argument oldfile) " " (shell-quote-argument newfile))
The following two functions are useful for combining a list of
individual command-line argument strings into a single string, and
taking a string apart into a list of individual command-line
arguments. These functions are mainly intended to be used for
converting user input in the minibuffer, a Lisp string, into a list of
string arguments to be passed to call-process or
start-process, or for the converting such lists of arguments in
a single Lisp string to be presented in the minibuffer or echo area.
This function splits string into substrings at matches for the regular expression separators, like
split-stringdoes (see Creating Strings); in addition, it removes quoting from the substrings. It then makes a list of the substrings and returns it.If separators is omitted or
nil, it defaults to"\\s-+", which is a regular expression that matches one or more characters with whitespace syntax (see Syntax Class Table).This function supports two types of quoting: enclosing a whole string in double quotes
"...", and quoting individual characters with a backslash escape ‘\’. The latter is also used in Lisp strings, so this function can handle those as well.
This function concatenates list-of-strings into a single string, quoting each string as necessary. It also sticks the separator string between each pair of strings; if separator is omitted or
nil, it defaults to" ". The return value is the resulting string.The strings in list-of-strings that need quoting are those that include separator as their substring. Quoting a string encloses it in double quotes
"...". In the simplest case, if you are consing a command from the individual command-line arguments, every argument that includes embedded blanks will be quoted.
After a synchronous process is created, Emacs waits for the
process to terminate before continuing. Starting Dired on GNU or
Unix16 is an example of this: it
runs ls in a synchronous process, then modifies the output
slightly. Because the process is synchronous, the entire directory
listing arrives in the buffer before Emacs tries to do anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing C-g. The first C-g tries to kill
the subprocess with a SIGINT signal; but it waits until the
subprocess actually terminates before quitting. If during that time the
user types another C-g, that kills the subprocess instantly with
SIGKILL and quits immediately (except on MS-DOS, where killing
other processes doesn't work). See Quitting.
The synchronous subprocess functions return an indication of how the process terminated.
The output from a synchronous subprocess is generally decoded using a
coding system, much like text read from a file. The input sent to a
subprocess by call-process-region is encoded using a coding
system, much like text written into a file. See Coding Systems.
This function calls program in a separate process and waits for it to finish.
The standard input for the process comes from file infile if infile is not
nil, and from the null device otherwise. The argument destination says where to put the process output. Here are the possibilities:
- a buffer
- Insert the output in that buffer, before point. This includes both the standard output stream and the standard error stream of the process.
- a string
- Insert the output in a buffer with that name, before point.
t- Insert the output in the current buffer, before point.
nil- Discard the output.
- 0
- Discard the output, and return
nilimmediately without waiting for the subprocess to finish.In this case, the process is not truly synchronous, since it can run in parallel with Emacs; but you can think of it as synchronous in that Emacs is essentially finished with the subprocess as soon as this function returns.
MS-DOS doesn't support asynchronous subprocesses, so this option doesn't work there.
(real-destination error-destination)- Keep the standard output stream separate from the standard error stream; deal with the ordinary output as specified by real-destination, and dispose of the error output according to error-destination. If error-destination is
nil, that means to discard the error output,tmeans mix it with the ordinary output, and a string specifies a file name to redirect error output into.You can't directly specify a buffer to put the error output in; that is too difficult to implement. But you can achieve this result by sending the error output to a temporary file and then inserting the file into a buffer.
If display is non-
nil, thencall-processredisplays the buffer as output is inserted. (However, if the coding system chosen for decoding output isundecided, meaning deduce the encoding from the actual data, then redisplay sometimes cannot continue once non-ASCII characters are encountered. There are fundamental reasons why it is hard to fix this; see Output from Processes.)Otherwise the function
call-processdoes no redisplay, and the results become visible on the screen only when Emacs redisplays that buffer in the normal course of events.The remaining arguments, args, are strings that specify command line arguments for the program.
The value returned by
call-process(unless you told it not to wait) indicates the reason for process termination. A number gives the exit status of the subprocess; 0 means success, and any other value means failure. If the process terminated with a signal,call-processreturns a string describing the signal.In the examples below, the buffer ‘foo’ is current.
(call-process "pwd" nil t) ⇒ 0 ---------- Buffer: foo ---------- /usr/user/lewis/manual ---------- Buffer: foo ---------- (call-process "grep" nil "bar" nil "lewis" "/etc/passwd") ⇒ 0 ---------- Buffer: bar ---------- lewis:5LTsHm66CSWKg:398:21:Bil Lewis:/user/lewis:/bin/csh ---------- Buffer: bar ----------Here is a good example of the use of
call-process, which used to be found in the definition ofinsert-directory:(call-process insert-directory-program nil t nil switches (if full-directory-p (concat (file-name-as-directory file) ".") file))
This function processes files synchronously in a separate process. It is similar to
call-processbut may invoke a file handler based on the value of the variabledefault-directory. The current working directory of the subprocess isdefault-directory.The arguments are handled in almost the same way as for
call-process, with the following differences:Some file handlers may not support all combinations and forms of the arguments infile, buffer, and display. For example, some file handlers might behave as if display were
nil, regardless of the value actually passed. As another example, some file handlers might not support separating standard output and error output by way of the buffer argument.If a file handler is invoked, it determines the program to run based on the first argument program. For instance, consider that a handler for remote files is invoked. Then the path that is used for searching the program might be different than
exec-path.The second argument infile may invoke a file handler. The file handler could be different from the handler chosen for the
process-filefunction itself. (For example,default-directorycould be on a remote host, whereas infile is on another remote host. Ordefault-directorycould be non-special, whereas infile is on a remote host.)If buffer is a list of the form
(real-destination error-destination), and error-destination names a file, then the same remarks as for infile apply.The remaining arguments (args) will be passed to the process verbatim. Emacs is not involved in processing file names that are present in args. To avoid confusion, it may be best to avoid absolute file names in args, but rather to specify all file names as relative to
default-directory. The functionfile-relative-nameis useful for constructing such relative file names.
This variable indicates, whether a call of
process-filechanges remote files.Per default, this variable is always set to
t, meaning that a call ofprocess-filecould potentially change any file on a remote host. When set tonil, a file handler could optimize its behaviour with respect to remote file attributes caching.This variable should never be changed by
setq. Instead of, it shall be set only by let-binding.
This function sends the text from start to end as standard input to a process running program. It deletes the text sent if delete is non-
nil; this is useful when destination ist, to insert the output in the current buffer in place of the input.The arguments destination and display control what to do with the output from the subprocess, and whether to update the display as it comes in. For details, see the description of
call-process, above. If destination is the integer 0,call-process-regiondiscards the output and returnsnilimmediately, without waiting for the subprocess to finish (this only works if asynchronous subprocesses are supported).The remaining arguments, args, are strings that specify command line arguments for the program.
The return value of
call-process-regionis just like that ofcall-process:nilif you told it to return without waiting; otherwise, a number or string which indicates how the subprocess terminated.In the following example, we use
call-process-regionto run thecatutility, with standard input being the first five characters in buffer ‘foo’ (the word ‘input’).catcopies its standard input into its standard output. Since the argument destination ist, this output is inserted in the current buffer.---------- Buffer: foo ---------- input-!- ---------- Buffer: foo ---------- (call-process-region 1 6 "cat" nil t) ⇒ 0 ---------- Buffer: foo ---------- inputinput-!- ---------- Buffer: foo ----------The
shell-command-on-regioncommand usescall-process-regionlike this:(call-process-region start end shell-file-name ; Name of program. nil ; Do not delete region. buffer ; Send output tobuffer. nil ; No redisplay during output. "-c" command) ; Arguments for the shell.
This function executes the shell command command synchronously in a separate process. The final arguments args are additional arguments to add at the end of command. The other arguments are handled as in
call-process.
This function is like
call-process-shell-command, but usesprocess-fileinternally. Depending ondefault-directory, command can be executed also on remote hosts.
This function executes command (a string) as a shell command, then returns the command's output as a string.
This function runs program in a separate process, waits for it to finish, and returns its output as a list of strings. Each string in the list holds a single line of text output by the program; the end-of-line characters are stripped from each line. The arguments beyond program, args, are strings that specify command-line arguments with which to run the program.
If program exits with a non-zero exit status, this function signals an error.
This function works by calling
call-process, so program output is decoded in the same way as forcall-process.
After an asynchronous process is created, Emacs and the subprocess both continue running immediately. The process thereafter runs in parallel with Emacs, and the two can communicate with each other using the functions described in the following sections. However, communication is only partially asynchronous: Emacs sends data to the process only when certain functions are called, and Emacs accepts data from the process only when Emacs is waiting for input or for a time delay.
Here we describe how to create an asynchronous process.
This function creates a new asynchronous subprocess and starts the program program running in it. It returns a process object that stands for the new subprocess in Lisp. The argument name specifies the name for the process object; if a process with this name already exists, then name is modified (by appending ‘<1>’, etc.) to be unique. The buffer buffer-or-name is the buffer to associate with the process.
The remaining arguments, args, are strings that specify command line arguments for the program.
In the example below, the first process is started and runs (rather, sleeps) for 100 seconds. Meanwhile, the second process is started, and given the name ‘my-process<1>’ for the sake of uniqueness. It inserts the directory listing at the end of the buffer ‘foo’, before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100") ⇒ #<process my-process> (start-process "my-process" "foo" "ls" "-l" "/user/lewis/bin") ⇒ #<process my-process<1>> ---------- Buffer: foo ---------- total 2 lrwxrwxrwx 1 lewis 14 Jul 22 10:12 gnuemacs --> /emacs -rwxrwxrwx 1 lewis 19 Jul 30 21:02 lemon Process my-process<1> finished Process my-process finished ---------- Buffer: foo ----------
Like
start-process, this function starts a new asynchronous subprocess running program in it, and returns its process object—whendefault-directoryis not a magic file name.If
default-directoryis magic, the function invokes its file handler instead. This handler ought to run program, perhaps on the local host, perhaps on a remote host that corresponds todefault-directory. In the latter case, the local part ofdefault-directorybecomes the working directory of the process.This function does not try to invoke file name handlers for program or for the program-args.
Depending on the implementation of the file handler, it might not be possible to apply
process-filterorprocess-sentinelto the resulting process object (see Filter Functions, see Sentinels).Some file handlers may not support
start-file-process(for exampleange-ftp-hook-function). In such cases, the function does nothing and returnsnil.
This function is like
start-processexcept that it uses a shell to execute the specified command. The argument command is a shell command name. The variableshell-file-namespecifies which shell to use.The point of running a program through the shell, rather than directly with
start-process, is so that you can employ shell features such as wildcards in the arguments. It follows that if you include an arbitrary user-specified arguments in the command, you should quote it withshell-quote-argumentfirst, so that any special shell characters do not have their special shell meanings. See Shell Arguments.
This function is like
start-process-shell-command, but usesstart-file-processinternally. By this, command can be executed also on remote hosts, depending ondefault-directory.
This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-
nil, then PTYs are used, when available. Otherwise, pipes are used.PTYs are usually preferable for processes visible to the user, as in Shell mode, because they allow job control (C-c, C-z, etc.) to work between the process and its children, whereas pipes do not. For subprocesses used for internal purposes by programs, it is often better to use a pipe, because they are more efficient. In addition, the total number of PTYs is limited on many systems and it is good not to waste them.
The value of
process-connection-typetakes effect whenstart-processis called. So you can specify how to communicate with one subprocess by binding the variable around the call tostart-process.(let ((process-connection-type nil)) ; Use a pipe. (start-process ...))To determine whether a given subprocess actually got a pipe or a PTY, use the function
process-tty-name(see Process Information).
Deleting a process disconnects Emacs immediately from the subprocess. Processes are deleted automatically after they terminate, but not necessarily right away. You can delete a process explicitly at any time. If you delete a terminated process explicitly before it is deleted automatically, no harm results. Deleting a running process sends a signal to terminate it (and its child processes if any), and calls the process sentinel if it has one. See Sentinels.
When a process is deleted, the process object itself continues to exist as long as other Lisp objects point to it. All the Lisp primitives that work on process objects accept deleted processes, but those that do I/O or send signals will report an error. The process mark continues to point to the same place as before, usually into a buffer where output from the process was being inserted.
This variable controls automatic deletion of processes that have terminated (due to calling
exitor to a signal). If it isnil, then they continue to exist until the user runslist-processes. Otherwise, they are deleted immediately after they exit.
This function deletes a process, killing it with a
SIGKILLsignal. The argument may be a process, the name of a process, a buffer, or the name of a buffer. (A buffer or buffer-name stands for the process thatget-buffer-processreturns.) Callingdelete-processon a running process terminates it, updates the process status, and runs the sentinel (if any) immediately. If the process has already terminated, callingdelete-processhas no effect on its status, or on the running of its sentinel (which will happen sooner or later).(delete-process "*shell*") ⇒ nil
Several functions return information about processes.
list-processes is provided for interactive use.
This command displays a listing of all living processes. In addition, it finally deletes any process whose status was ‘Exited’ or ‘Signaled’. It returns
nil.If query-only is non-
nilthen it lists only processes whose query flag is non-nil. See Query Before Exit.
This function returns a list of all processes that have not been deleted.
(process-list) ⇒ (#<process display-time> #<process shell>)
This function returns the process named name, or
nilif there is none. An error is signaled if name is not a string.(get-process "shell") ⇒ #<process shell>
This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program.
(process-command (get-process "shell")) ⇒ ("/bin/csh" "-i")
This function returns information about how a network or serial process was set up. For a network process, when key is
nil, it returns(hostname service)which specifies what you connected to. For a serial process, when key isnil, it returns(port speed). For an ordinary child process, this function always returnst.If key is
t, the value is the complete status information for the connection, server, or serial port; that is, the list of keywords and values specified inmake-network-processormake-serial-process, except that some of the values represent the current status instead of what you specified.For a network process:
:buffer- The associated value is the process buffer.
:filter- The associated value is the process filter function.
:sentinel- The associated value is the process sentinel function.
:remote- In a connection, the address in internal format of the remote peer.
:local- The local address, in internal format.
:service- In a server, if you specified
tfor service, this value is the actual port number.
:localand:remoteare included even if they were not specified explicitly inmake-network-process.For a serial process, see
make-serial-processandserial-process-configurefor a list of keys.If key is a keyword, the function returns the value corresponding to that keyword.
This function returns the PID of process. This is an integer that distinguishes the process process from all other processes running on the same computer at the current time. The PID of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists.
This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, or a process name (a string).
The possible values for an actual subprocess are:
run- for a process that is running.
stop- for a process that is stopped but continuable.
exit- for a process that has exited.
signal- for a process that has received a fatal signal.
open- for a network connection that is open.
closed- for a network connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place.
connect- for a non-blocking connection that is waiting to complete.
failed- for a non-blocking connection that has failed to complete.
listen- for a network server that is listening.
nil- if process-name is not the name of an existing process.
(process-status (get-buffer "*shell*")) ⇒ run x ⇒ #<process xx<1>> (process-status x) ⇒ exitFor a network connection,
process-statusreturns one of the symbolsopenorclosed. The latter means that the other side closed the connection, or Emacs diddelete-process.
This function returns the symbol
networkfor a network connection or server,serialfor a serial port connection, orrealfor a real subprocess.
This function returns the exit status of process or the signal number that killed it. (Use the result of
process-statusto determine which of those it is.) If process has not yet terminated, the value is 0.
This function returns the terminal name that process is using for its communication with Emacs—or
nilif it is using pipes instead of a terminal (seeprocess-connection-typein Asynchronous Processes).
This function returns a cons cell describing the coding systems in use for decoding output from process and for encoding input to process (see Coding Systems). The value has this form:
(coding-system-for-decoding . coding-system-for-encoding)
This function specifies the coding systems to use for subsequent output from and input to process. It will use decoding-system to decode subprocess output, and encoding-system to encode subprocess input.
Every process also has a property list that you can use to store miscellaneous values associated with the process.
This function returns the value of the propname property of process.
This function sets the value of the propname property of process to value.
This function sets the process plist of process to plist.
Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the “standard input” of the subprocess.
Some operating systems have limited space for buffered input in a PTY. On these systems, Emacs sends an EOF periodically amidst the other characters, to force them through. For most programs, these EOFs do no harm.
Subprocess input is normally encoded using a coding system before the
subprocess receives it, much like text written into a file. You can use
set-process-coding-system to specify which coding system to use
(see Process Information). Otherwise, the coding system comes from
coding-system-for-write, if that is non-nil; or else from
the defaulting mechanism (see Default Coding Systems).
Sometimes the system is unable to accept input for that process, because the input buffer is full. When this happens, the send functions wait a short while, accepting output from subprocesses, and then try again. This gives the subprocess a chance to read more of its pending input and make space in the buffer. It also allows filters, sentinels and timers to run—so take account of that in writing your code.
In these functions, the process argument can be a process or
the name of a process, or a buffer or buffer name (which stands
for a process via get-buffer-process). nil means
the current buffer's process.
This function sends process the contents of string as standard input. If it is
nil, the current buffer's process is used.The function returns
nil.(process-send-string "shell<1>" "ls\n") ⇒ nil ---------- Buffer: *shell* ---------- ... introduction.texi syntax-tables.texi~ introduction.texi~ text.texi introduction.txt text.texi~ ... ---------- Buffer: *shell* ----------
This function sends the text in the region defined by start and end as standard input to process.
An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)
This function makes process see an end-of-file in its input. The EOF comes after any text already sent to it.
The function returns process.
(process-send-eof "shell") ⇒ "shell"
This function will tell you whether a process has given control of its terminal to its own child process. The value is
tif this is true, or if Emacs cannot tell; it isnilif Emacs can be certain that this is not so.
Sending a signal to a subprocess is a way of interrupting its
activities. There are several different signals, each with its own
meaning. The set of signals and their names is defined by the operating
system. For example, the signal SIGINT means that the user has
typed C-c, or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop or resume execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.
You can send signals explicitly by calling the functions in this
section. Emacs also sends signals automatically at certain times:
killing a buffer sends a SIGHUP signal to all its associated
processes; killing Emacs sends a SIGHUP signal to all remaining
processes. (SIGHUP is a signal that usually indicates that the
user hung up the phone.)
Each of the signal-sending functions takes two optional arguments: process and current-group.
The argument process must be either a process, a process
name, a buffer, a buffer name, or nil. A buffer or buffer name
stands for a process through get-buffer-process. nil
stands for the process associated with the current buffer. An error
is signaled if process does not identify a process.
The argument current-group is a flag that makes a difference
when you are running a job-control shell as an Emacs subprocess. If it
is non-nil, then the signal is sent to the current process-group
of the terminal that Emacs uses to communicate with the subprocess. If
the process is a job-control shell, this means the shell's current
subjob. If it is nil, the signal is sent to the process group of
the immediate subprocess of Emacs. If the subprocess is a job-control
shell, this is the shell itself.
The flag current-group has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes. For the same reason,
job-control shells won't work when a pipe is used. See
process-connection-type in Asynchronous Processes.
This function interrupts the process process by sending the signal
SIGINT. Outside of Emacs, typing the “interrupt character” (normally C-c on some systems, andDELon others) sends this signal. When the argument current-group is non-nil, you can think of this function as “typing C-c” on the terminal by which Emacs talks to the subprocess.
This function kills the process process by sending the signal
SIGKILL. This signal kills the subprocess immediately, and cannot be handled by the subprocess.
This function sends the signal
SIGQUITto the process process. This signal is the one sent by the “quit character” (usually C-b or C-\) when you are not inside Emacs.
This function stops the process process by sending the signal
SIGTSTP. Usecontinue-processto resume its execution.Outside of Emacs, on systems with job control, the “stop character” (usually C-z) normally sends this signal. When current-group is non-
nil, you can think of this function as “typing C-z” on the terminal Emacs uses to communicate with the subprocess.
This function resumes execution of the process process by sending it the signal
SIGCONT. This presumes that process was stopped previously.
This function sends a signal to process process. The argument signal specifies which signal to send; it should be an integer.
The process argument can be a system process ID; that allows you to send signals to processes that are not children of Emacs. See System Processes.
There are two ways to receive the output that a subprocess writes to its standard output stream. The output can be inserted in a buffer, which is called the associated buffer of the process, or a function called the filter function can be called to act on the output. If the process has no buffer and no filter function, its output is discarded.
When a subprocess terminates, Emacs reads any pending output, then stops reading output from that subprocess. Therefore, if the subprocess has children that are still live and still producing output, Emacs won't receive that output.
Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input, in sit-for and sleep-for
(see Waiting), and in accept-process-output (see Accepting Output). This minimizes the problem of timing errors that usually
plague parallel programming. For example, you can safely create a
process and only then specify its buffer or filter function; no output
can arrive before you finish, if the code in between does not call any
primitive that waits.
On some systems, when Emacs reads the output from a subprocess, the output data is read in very small blocks, potentially resulting in very poor performance. This behavior can be remedied to some extent by setting the variable process-adaptive-read-buffering to a non-
nilvalue (the default), as it will automatically delay reading from such processes, thus allowing them to produce more output before Emacs tries to read it.
It is impossible to separate the standard output and standard error streams of the subprocess, because Emacs normally spawns the subprocess inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If you want to keep the output to those streams separate, you should redirect one of them to a file—for example, by using an appropriate shell command.
A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp.
Unless the process has a filter function (see Filter Functions),
its output is inserted in the associated buffer. The position to insert
the output is determined by the process-mark, which is then
updated to point to the end of the text just inserted. Usually, but not
always, the process-mark is at the end of the buffer.
Killing the associated buffer of a process also kills the process.
Emacs asks for confirmation first, if the process's
process-query-on-exit-flag is non-nil (see Query Before Exit). This confirmation is done by the function
process-kill-buffer-query-function, which is run from
kill-buffer-query-functions (see Killing Buffers).
This function returns the associated buffer of the process process.
(process-buffer (get-process "shell")) ⇒ #<buffer *shell*>
This function returns the process marker for process, which is the marker that says where to insert output from the process.
If process does not have a buffer,
process-markreturns a marker that points nowhere.Insertion of process output in a buffer uses this marker to decide where to insert, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively.
Filter functions normally should use this marker in the same fashion as is done by direct insertion of output in the buffer. A good example of a filter function that uses
process-markis found at the end of the following section.When the user is expected to enter input in the process buffer for transmission to the process, the process marker separates the new input from previous output.
This function sets the buffer associated with process to buffer. If buffer is
nil, the process becomes associated with no buffer.
This function returns a nondeleted process associated with the buffer specified by buffer-or-name. If there are several processes associated with it, this function chooses one (currently, the one most recently created, but don't count on that). Deletion of a process (see
delete-process) makes it ineligible for this function to return.It is usually a bad idea to have more than one process associated with the same buffer.
(get-buffer-process "*shell*") ⇒ #<process shell>Killing the process's buffer deletes the process, which kills the subprocess with a
SIGHUPsignal (see Signals to Processes).
A process filter function is a function that receives the standard output from the associated process. If a process has a filter, then all output from that process is passed to the filter. The process buffer is used directly for output from the process only when there is no filter.
The filter function can only be called when Emacs is waiting for
something, because process output arrives only at such times. Emacs
waits when reading terminal input, in sit-for and
sleep-for (see Waiting), and in accept-process-output
(see Accepting Output).
A filter function must accept two arguments: the associated process and a string, which is output just received from it. The function is then free to do whatever it chooses with the output.
Quitting is normally inhibited within a filter function—otherwise,
the effect of typing C-g at command level or to quit a user
command would be unpredictable. If you want to permit quitting inside
a filter function, bind inhibit-quit to nil. In most
cases, the right way to do this is with the macro
with-local-quit. See Quitting.
If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started. However, if
debug-on-error is non-nil, the error-catching is turned
off. This makes it possible to use the Lisp debugger to debug the
filter function. See Debugger.
Many filter functions sometimes or always insert the text in the
process's buffer, mimicking the actions of Emacs when there is no
filter. Such filter functions need to use set-buffer in order to
be sure to insert in that buffer. To avoid setting the current buffer
semipermanently, these filter functions must save and restore the
current buffer. They should also update the process marker, and in some
cases update the value of point. Here is how to do these things:
(defun ordinary-insertion-filter (proc string)
(with-current-buffer (process-buffer proc)
(let ((moving (= (point) (process-mark proc))))
(save-excursion
;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc))))))
The reason to use with-current-buffer, rather than using
save-excursion to save and restore the current buffer, is so as
to preserve the change in point made by the second call to
goto-char.
To make the filter force the process buffer to be visible whenever new
text arrives, insert the following line just before the
with-current-buffer construct:
(display-buffer (process-buffer proc))
To force point to the end of the new output, no matter where it was
previously, eliminate the variable moving and call
goto-char unconditionally.
In earlier Emacs versions, every filter function that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for filter functions; they never need to do it explicitly. See Match Data.
A filter function that writes the output into the buffer of the
process should check whether the buffer is still alive. If it tries to
insert into a dead buffer, it will get an error. The expression
(buffer-name (process-buffer process)) returns nil
if the buffer is dead.
The output to the function may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. If the filter looks for certain text strings in the subprocess output, make sure to handle the case where one of these strings is split across two or more batches of output; one way to do this is to insert the received text into a temporary buffer, which can then be searched.
This function gives process the filter function filter. If filter is
nil, it gives the process no filter.
This function returns the filter function of process, or
nilif it has none.
Here is an example of use of a filter function:
(defun keep-output (process output)
(setq kept (cons output kept)))
⇒ keep-output
(setq kept nil)
⇒ nil
(set-process-filter (get-process "shell") 'keep-output)
⇒ keep-output
(process-send-string "shell" "ls ~/other\n")
⇒ nil
kept
⇒ ("lewis@slug[8] % "
"FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
address.txt backup.psf kolstad.psf
backup.bib~ david.mss resume-Dec-86.mss~
backup.err david.psf resume-Dec.psf
backup.mss dland syllabus.mss
"
"#backups.mss# backup.mss~ kolstad.mss
")
When Emacs writes process output directly into a multibyte buffer,
it decodes the output according to the process output coding system.
If the coding system is raw-text or no-conversion, Emacs
converts the unibyte output to multibyte using
string-to-multibyte, and inserts the resulting multibyte text.
You can use set-process-coding-system to specify which coding
system to use (see Process Information). Otherwise, the coding
system comes from coding-system-for-read, if that is
non-nil; or else from the defaulting mechanism (see Default Coding Systems). If the text output by a process contains null
bytes, Emacs by default uses no-conversion for it; see
inhibit-null-byte-detection, for how to
control this behavior.
Warning: Coding systems such as undecided which
determine the coding system from the data do not work entirely
reliably with asynchronous subprocess output. This is because Emacs
has to process asynchronous subprocess output in batches, as it
arrives. Emacs must try to detect the proper coding system from one
batch at a time, and this does not always work. Therefore, if at all
possible, specify a coding system that determines both the character
code conversion and the end of line conversion—that is, one like
latin-1-unix, rather than undecided or latin-1.
When Emacs calls a process filter function, it provides the process
output as a multibyte string or as a unibyte string according to the
process's filter coding system. Emacs
decodes the output according to the process output coding system,
which usually produces a multibyte string, except for coding systems
such as binary and raw-text
Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process.
This function allows Emacs to read pending output from processes. The output is inserted in the associated buffers or given to their filter functions. If process is non-
nilthen this function does not return until some output has been received from process.The arguments seconds and millisec let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds. The two time periods thus specified are added together, and
accept-process-outputreturns after that much time, whether or not there has been any subprocess output.The argument millisec is semi-obsolete nowadays because seconds can be a floating point number to specify waiting a fractional number of seconds. If seconds is 0, the function accepts whatever output is pending but does not wait.
If process is a process, and the argument just-this-one is non-
nil, only output from that process is handled, suspending output from other processes until some output has been received from that process or the timeout expires. If just-this-one is an integer, also inhibit running timers. This feature is generally not recommended, but may be necessary for specific applications, such as speech synthesis.The function
accept-process-outputreturns non-nilif it did get some output, ornilif the timeout expired before output arrived.
A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.
The string describing the event looks like one of the following:
"finished\n".
"exited abnormally with code exitcode\n".
"name-of-signal\n".
"name-of-signal (core dumped)\n".
A sentinel runs only while Emacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output). This avoids the
timing errors that could result from running them at random places in
the middle of other Lisp programs. A program can wait, so that
sentinels will run, by calling sit-for or sleep-for
(see Waiting), or accept-process-output (see Accepting Output). Emacs also allows sentinels to run when the command loop is
reading input. delete-process calls the sentinel when it
terminates a running process.
Emacs does not keep a queue of multiple reasons to call the sentinel of one process; it records just the current status and the fact that there has been a change. Therefore two changes in status, coming in quick succession, can call the sentinel just once. However, process termination will always run the sentinel exactly once. This is because the process status can't change again after termination.
Emacs explicitly checks for output from the process before running the process sentinel. Once the sentinel runs due to process termination, no further output can arrive from the process.
A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive. If it tries to insert
into a dead buffer, it will get an error. If the buffer is dead,
(buffer-name (process-buffer process)) returns nil.
Quitting is normally inhibited within a sentinel—otherwise, the
effect of typing C-g at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a
sentinel, bind inhibit-quit to nil. In most cases, the
right way to do this is with the macro with-local-quit.
See Quitting.
If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started. However, if
debug-on-error is non-nil, the error-catching is turned
off. This makes it possible to use the Lisp debugger to debug the
sentinel. See Debugger.
While a sentinel is running, the process sentinel is temporarily
set to nil so that the sentinel won't run recursively.
For this reason it is not possible for a sentinel to specify
a new sentinel.
In earlier Emacs versions, every sentinel that did regular expression searching or matching had to explicitly save and restore the match data. Now Emacs does this automatically for sentinels; they never need to do it explicitly. See Match Data.
This function associates sentinel with process. If sentinel is
nil, then the process will have no sentinel. The default behavior when there is no sentinel is to insert a message in the process's buffer when the process status changes.Changes in process sentinel take effect immediately—if the sentinel is slated to be run but has not been called yet, and you specify a new sentinel, the eventual call to the sentinel will use the new one.
(defun msg-me (process event) (princ (format "Process: %s had the event `%s'" process event))) (set-process-sentinel (get-process "shell") 'msg-me) ⇒ msg-me (kill-process (get-process "shell")) -| Process: #<process shell> had the event `killed' ⇒ #<process shell>
This function returns the sentinel of process, or
nilif it has none.
While a sentinel or filter function is running, this function returns non-
nilif Emacs was waiting for keyboard input from the user at the time the sentinel or filter function was called,nilif it was not.
When Emacs exits, it terminates all its subprocesses by sending them
the SIGHUP signal. Because subprocesses may be doing
valuable work, Emacs normally asks the user to confirm that it is ok
to terminate them. Each process has a query flag which, if
non-nil, says that Emacs should ask for confirmation before
exiting and thus killing that process. The default for the query flag
is t, meaning do query.
This function sets the query flag of process to flag. It returns flag.
;; Don't query about the shell process (set-process-query-on-exit-flag (get-process "shell") nil) ⇒ t
This function clears the query flag of process, so that Emacs will not query the user on account of that process.
Actually, the function does more than that: it returns the old value of the process's query flag, and sets the query flag to do-query. Please don't use this function to do those things any more—please use the newer, cleaner functions
process-query-on-exit-flagandset-process-query-on-exit-flagin all but the simplest cases. The only way you should useprocess-kill-without-querynowadays is like this:;; Don't query about the shell process (process-kill-without-query (get-process "shell"))
In addition to accessing and manipulating processes that are subprocesses of the current Emacs session, Emacs Lisp programs can also access other processes running on the same machine. We call these system processes, to distinguish between them and Emacs subprocesses.
Emacs provides several primitives for accessing system processes.
Not all platforms support these primitives; on those which don't,
these primitives return nil.
This function returns a list of all the processes running on the system. Each process is identified by its PID, a numerical process ID that is assigned by the OS and distinguishes the process from all the other processes running on the same machine at the same time.
This function returns an alist of attributes for the process specified by its process ID pid. Each association in the alist is of the form
(key.value), where key designates the attribute and value is the value of that attribute. The various attribute key's that this function can return are listed below. Not all platforms support all of these attributes; if an attribute is not supported, its association will not appear in the returned alist. Values that are numbers can be either integer or floating-point, depending on the magnitude of the value.
euid- The effective user ID of the user who invoked the process. The corresponding value is a number. If the process was invoked by the same user who runs the current Emacs session, the value is identical to what
user-uidreturns (see User Identification).user- User name corresponding to the process's effective user ID, a string.
egid- The group ID of the effective user ID, a number.
group- Group name corresponding to the effective user's group ID, a string.
comm- The name of the command that runs in the process. This is a string that usually specifies the name of the executable file of the process, without the leading directories. However, some special system processes can report strings that do not correspond to an executable file of a program.
state- The state code of the process. This is a short string that encodes the scheduling state of the process. Here's a list of the most frequently seen codes:
"D"- uninterruptible sleep (usually I/O)
"R"- running
"S"- interruptible sleep (waiting for some event)
"T"- stopped, e.g., by a job control signal
"Z"- “zombie”: a process that terminated, but was not reaped by its parent
For the full list of the possible states, see the manual page of the ps command.
ppid- The process ID of the parent process, a number.
pgrp- The process group ID of the process, a number.
sess- The session ID of the process. This is a number that is the process ID of the process's session leader.
ttname- A string that is the name of the process's controlling terminal. On Unix and GNU systems, this is normally the file name of the corresponding terminal device, such as /dev/pts65.
tpgid- The numerical process group ID of the foreground process group that uses the process's terminal.
minflt- The number of minor page faults caused by the process since its beginning. (Minor page faults are those that don't involve reading from disk.)
majflt- The number of major page faults caused by the process since its beginning. (Major page faults require a disk to be read, and are thus more expensive than minor page faults.)
cminfltcmajflt- Like
minfltandmajflt, but include the number of page faults for all the child processes of the given process.utime- Time spent by the process in the user context, for running the application's code. The corresponding value is in the
(highlowmicrosec)format, the same format used by functionscurrent-time(see current-time) andfile-attributes(see File Attributes).stime- Time spent by the process in the system (kernel) context, for processing system calls. The corresponding value is in the same format as for
utime.time- The sum of
utimeandstime. The corresponding value is in the same format as forutime.cutimecstimectime- Like
utime,stime, andtime, but include the times of all the child processes of the given process.pri- The numerical priority of the process.
nice- The nice value of the process, a number. (Processes with smaller nice values get scheduled more favorably.)
thcount- The number of threads in the process.
start- The time the process was started, in the
(highlowmicrosec)format used bycurrent-timeandfile-attributes.etime- The time elapsed since the process started, in the
(highlowmicrosec)format.vsize- The virtual memory size of the process, measured in kilobytes.
rss- The size of the process's resident set, the number of kilobytes occupied by the process in the machine's physical memory.
pcpu- The percentage of the CPU time used by the process since it started. The corresponding value is a floating-point number between 0 and 100.
pmem- The percentage of the total physical memory installed on the machine used by the process's resident set. The value is a floating-point number between 0 and 100.
args- The command-line with which the process was invoked. This is a string in which individual command-line arguments are separated by blanks; whitespace characters that are embedded in the arguments are quoted as appropriate for the system's shell: escaped by backslash characters on GNU and Unix, and enclosed in double quote characters on Windows. Thus, this command-line string can be directly used in primitives such as
shell-command.
You can use a transaction queue to communicate with a subprocess
using transactions. First use tq-create to create a transaction
queue communicating with a specified process. Then you can call
tq-enqueue to send a transaction.
This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine.
This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.
The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.
The argument regexp is a regular expression that should match text at the end of the entire answer, but nothing before; that's how
tq-enqueuedetermines where the answer ends.If the argument delay-question is non-
nil, delay sending this question until the process has finished replying to any previous questions. This produces more reliable results with some processes.The return value of
tq-enqueueitself is not meaningful.
Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.
Transaction queues are implemented by means of a filter function. See Filter Functions.
Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
connections to other processes on the same machine or other machines.
A network connection is handled by Lisp much like a subprocess, and is
represented by a process object. However, the process you are
communicating with is not a child of the Emacs process, so it has no
process ID, and you can't kill it or send it signals. All you
can do is send and receive data. delete-process closes the
connection, but does not kill the program at the other end; that
program must decide what to do about closure of the connection.
Lisp programs can listen for connections by creating network servers. A network server is also represented by a kind of process object, but unlike a network connection, the network server never transfers data itself. When it receives a connection request, it creates a new network connection to represent the connection just made. (The network connection inherits certain information, including the process plist, from the server.) The network server then goes back to listening for more connection requests.
Network connections and servers are created by calling
make-network-process with an argument list consisting of
keyword/argument pairs, for example :server t to create a
server process, or :type 'datagram to create a datagram
connection. See Low-Level Network, for details. You can also use
the open-network-stream function described below.
To distinguish the different types of processes, the
process-type function returns the symbol network for a
network connection or server, serial for a serial port
connection, or real for a real subprocess.
The process-status function returns open,
closed, connect, and failed for network
connections. For a network server, the status is always
listen. None of those values is possible for a real
subprocess. See Process Information.
You can stop and resume operation of a network process by calling
stop-process and continue-process. For a server
process, being stopped means not accepting new connections. (Up to 5
connection requests will be queued for when you resume the server; you
can increase this limit, unless it is imposed by the operating
system.) For a network stream connection, being stopped means not
processing input (any arriving input waits until you resume the
connection). For a datagram connection, some number of packets may be
queued but input may be lost. You can use the function
process-command to determine whether a network connection or
server is stopped; a non-nil value means yes.
This function opens a TCP connection, and returns a process object that represents the connection.
The name argument specifies the name for the process object. It is modified as necessary to make it unique.
The buffer-or-name argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify a filter function to handle the output. If buffer-or-name is
nil, it means that the connection is not associated with any buffer.The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer).
You create a server by calling make-network-process with
:server t. The server will listen for connection requests from
clients. When it accepts a client connection request, that creates a
new network connection, itself a process object, with the following
parameters:
nil, the connection process does
not get a separate process buffer; otherwise, Emacs creates a new
buffer for the purpose. The buffer name is the server's buffer name
or process name, concatenated with the client identification string.
The server's process buffer value is never used directly by Emacs, but it is passed to the log function, which can log connections by inserting text there.
process-contact
keywords :host, :service, :remote.
A datagram connection communicates with individual packets rather
than streams of data. Each call to process-send sends one
datagram packet (see Input to Processes), and each datagram
received results in one call to the filter function.
The datagram connection doesn't have to talk with the same remote
peer all the time. It has a remote peer address which specifies
where to send datagrams to. Each time an incoming datagram is passed
to the filter function, the peer address is set to the address that
datagram came from; that way, if the filter function sends a datagram,
it will go back to that place. You can specify the remote peer
address when you create the datagram connection using the
:remote keyword. You can change it later on by calling
set-process-datagram-address.
If process is a datagram connection or server, this function returns its remote peer address.
If process is a datagram connection or server, this function sets its remote peer address to address.
You can also create network connections by operating at a lower
level than that of open-network-stream, using
make-network-process.
make-network-processThe basic function for creating network connections and network
servers is make-network-process. It can do either of those
jobs, depending on the arguments you give it.
This function creates a network connection or server and returns the process object that represents it. The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value
nil, except for:coding,:filter-multibyte, and:reuseaddr. Here are the meaningful keywords:
- :name name
- Use the string name as the process name. It is modified if necessary to make it unique.
- :type type
- Specify the communication type. A value of
nilspecifies a stream connection (the default);datagramspecifies a datagram connection;seqpacketspecifies a “sequenced packet stream” connection. Both connections and servers can be of these types.- :server server-flag
- If server-flag is non-
nil, create a server. Otherwise, create a connection. For a stream type server, server-flag may be an integer which then specifies the length of the queue of pending connections to the server. The default queue length is 5.- :host host
- Specify the host to connect to. host should be a host name or Internet address, as a string, or the symbol
localto specify the local host. If you specify host for a server, it must specify a valid address for the local host, and only clients connecting to that address will be accepted.- :service service
- service specifies a port number to connect to, or, for a server, the port number to listen on. It should be a service name that translates to a port number, or an integer specifying the port number directly. For a server, it can also be
t, which means to let the system select an unused port number.- :family family
- family specifies the address (and protocol) family for communication.
nilmeans determine the proper address family automatically for the given host and service.localspecifies a Unix socket, in which case host is ignored.ipv4andipv6specify to use IPv4 and IPv6 respectively.- :local local-address
- For a server process, local-address is the address to listen on. It overrides family, host and service, and you may as well not specify them.
- :remote remote-address
- For a connection, remote-address is the address to connect to. It overrides family, host and service, and you may as well not specify them.
For a datagram server, remote-address specifies the initial setting of the remote datagram address.
The format of local-address or remote-address depends on the address family:
- An IPv4 address is represented as a five-element vector of four 8-bit integers and one 16-bit integer
[a b c d p]corresponding to numeric IPv4 address a.b.c.d and port number p.- An IPv6 address is represented as a nine-element vector of 16-bit integers
[a b c d e f g h p]corresponding to numeric IPv6 address a:b:c:d:e:f:g:h and port number p.- A local address is represented as a string which specifies the address in the local address space.
- An “unsupported family” address is represented by a cons
(f.av), where f is the family number and av is a vector specifying the socket address using one element per address data byte. Do not rely on this format in portable code, as it may depend on implementation defined constants, data sizes, and data structure alignment.- :nowait bool
- If bool is non-
nilfor a stream connection, return without waiting for the connection to complete. When the connection succeeds or fails, Emacs will call the sentinel function, with a second argument matching"open"(if successful) or"failed". The default is to block, so thatmake-network-processdoes not return until the connection has succeeded or failed.- :stop stopped
- Start the network connection or server in the `stopped' state if stopped is non-
nil.- :buffer buffer
- Use buffer as the process buffer.
- :coding coding
- Use coding as the coding system for this process. To specify different coding systems for decoding data from the connection and for encoding data sent to it, specify
(decoding.encoding)for coding.If you don't specify this keyword at all, the default is to determine the coding systems from the data.
- :noquery query-flag
- Initialize the process query flag to query-flag. See Query Before Exit.
- :filter filter
- Initialize the process filter to filter.
- :sentinel sentinel
- Initialize the process sentinel to sentinel.
- :log log
- Initialize the log function of a server process to log. The log function is called each time the server accepts a network connection from a client. The arguments passed to the log function are server, connection, and message, where server is the server process, connection is the new process for the connection, and message is a string describing what has happened.
- :plist plist
- Initialize the process plist to plist.
The original argument list, modified with the actual connection information, is available via the
process-contactfunction.
The following network options can be specified when you create a
network process. Except for :reuseaddr, you can also set or
modify these options later, using set-network-process-option.
For a server process, the options specified with
make-network-process are not inherited by the client
connections, so you will need to set the necessary options for each
child connection as it is created.
network-interface-list), only handle
packets received on that interface. If device-name is nil
(the default), handle packets received on any interface.
Using this option may require special privileges on some systems.
nil for a datagram process, the
process will receive datagram packet sent to a broadcast address, and
be able to send packets to a broadcast address. Ignored for a stream
connection.
nil, the process can only send
to hosts on the same network as the local host.
nil for a stream connection,
enable exchange of low-level keep-alive messages.
nil, wait for successful
transmission of all queued packets on the connection before it is
deleted (see delete-process). If linger-arg is an
integer, it specifies the maximum time in seconds to wait for queued
packets to be sent before closing the connection. Default is
nil which means to discard unsent queued packets when the
process is deleted.
nil for a stream connection,
receive out-of-band data in the normal data stream. Otherwise, ignore
out-of-band data.
nil (the default) for a stream
server process, allow this server to reuse a specific port number (see
:service) unless another process on this host is already
listening on that port. If reuseaddr-flag is nil, there
may be a period of time after the last use of that port (by any
process on the host), where it is not possible to make a new server on
that port.
This function sets or modifies a network option for network process process. See
make-network-processfor details of options option and their corresponding values value. If no-error is non-nil, this function returnsnilinstead of signaling an error if option is not a supported option. If the function successfully completes, it returnst.The current setting of an option is available via the
process-contactfunction.
To test for the availability of a given network feature, use
featurep like this:
(featurep 'make-network-process '(keyword value))
The result of the first form is t if it works to specify
keyword with value value in make-network-process.
The result of the second form is t if keyword is
supported by make-network-process. Here are some of the
keyword—value pairs you can test in
this way.
(:nowait t)nil if non-blocking connect is supported.
(:type datagram)nil if datagrams are supported.
(:family local)nil if local (a.k.a. “UNIX domain”) sockets are supported.
(:family ipv6)nil if IPv6 is supported.
(:service t)nil if the system can select the port for a server.
To test for the availability of a given network option, use
featurep like this:
(featurep 'make-network-process 'keyword)
Here are some of the options you can test in this way.
:bindtodevice:broadcast:dontroute:keepalive:linger:oobinline:priority:reuseaddrmake-network-process and set-network-process-option.
These additional functions are useful for creating and operating on network connections. Note that they are supported only on some systems.
This function returns a list describing the network interfaces of the machine you are using. The value is an alist whose elements have the form
(name.address). address has the same form as the local-address and remote-address arguments tomake-network-process.
This function returns information about the network interface named ifname. The value is a list of the form
(addr bcast netmask hwaddr flags).
- addr
- The Internet protocol address.
- bcast
- The broadcast address.
- netmask
- The network mask.
- hwaddr
- The layer 2 address (Ethernet MAC address, for instance).
- flags
- The current flags of the interface.
This function converts the Lisp representation of a network address to a string.
A five-element vector
[a b c d p]represents an IPv4 address a.b.c.d and port number p.format-network-addressconverts that to the string"a.b.c.d:p".A nine-element vector
[a b c d e f g h p]represents an IPv6 address along with a port number.format-network-addressconverts that to the string"[a:b:c:d:e:f:g:h]:p".If the vector does not include the port number, p, or if omit-port is non-
nil, the result does not include the:p suffix.
Emacs can communicate with serial ports. For interactive use,
M-x serial-term opens a terminal window. In a Lisp program,
make-serial-process creates a process object.
The serial port can be configured at run-time, without having to
close and re-open it. The function serial-process-configure
lets you change the speed, bytesize, and other parameters. In a
terminal window created by serial-term, you can click on the
mode line for configuration.
A serial connection is represented by a process object which can be
used similar to a subprocess or network process. You can send and
receive data and configure the serial port. A serial process object
has no process ID, you can't send signals to it, and the status codes
are different from other types of processes.
delete-process on the process object or kill-buffer on
the process buffer close the connection, but this does not affect the
device connected to the serial port.
The function process-type returns the symbol serial
for a process object representing a serial port connection.
Serial ports are available on GNU/Linux, Unix, and Windows systems.
Start a terminal-emulator for a serial port in a new buffer. port is the name of the serial port to which to connect. For example, this could be /dev/ttyS0 on Unix. On Windows, this could be COM1, or \\.\COM10 (double the backslashes in Lisp strings).
speed is the speed of the serial port in bits per second. 9600 is a common value. The buffer is in Term mode; see Term Mode, for the commands to use in that buffer. You can change the speed and the configuration in the mode line menu.
This function creates a process and a buffer. Arguments are specified as keyword/argument pairs. Here's the list of the meaningful keywords:
:portport (mandatory)- This is the name of the serial port. On Unix and GNU systems, this is a file name such as /dev/ttyS0. On Windows, this could be COM1, or \\.\COM10 for ports higher than COM9 (double the backslashes in Lisp strings).
:speedspeed (mandatory)- The speed of the serial port in bits per second. This function calls
serial-process-configureto handle the speed.:namename- The name of the process. If name is not given, port will serve as the process name as well.
:bufferbuffer- The buffer to associate with the process. The value could be either a buffer or a string that names a buffer. Process output goes at the end of that buffer, unless you specify an output stream or filter function to handle the output. If buffer is not given, the process buffer's name is taken from the value of the
:namekeyword.:codingcoding- If coding is a symbol, it specifies the coding system used for both reading and writing for this process. If coding is a cons
(decoding . encoding), decoding is used for reading, and encoding is used for writing. If not specified, the default is to determine the coding systems from data itself.:noqueryquery-flag- Initialize the process query flag to query-flag. See Query Before Exit. The flags defaults to
nilif unspecified.:stopbool- Start process in the
stoppedstate if bool is non-nil. In the stopped state, a serial process does not accept incoming data, but you can send outgoing data. The stopped state is cleared bycontinue-processand set bystop-process.:filterfilter- Install filter as the process filter.
:sentinelsentinel- Install sentinel as the process sentinel.
:plistplist- Install plist as the initial plist of the process.
:speed:bytesize:parity:stopbits:flowcontrol- These arguments are handled by
serial-process-configure, which is called bymake-serial-process.The original argument list, possibly modified by later configuration, is available via the function
process-contact.Examples:
(make-serial-process :port "/dev/ttyS0" :speed 9600) (make-serial-process :port "COM1" :speed 115200 :stopbits 2) (make-serial-process :port "\\\\.\\COM13" :speed 1200 :bytesize 7 :parity 'odd) (make-serial-process :port "/dev/tty.BlueConsole-SPP-1" :speed nil)
This functions configures a serial port connection. Arguments are specified as keyword/argument pairs. Attributes that are not given are re-initialized from the process's current configuration (available via the function
process-contact) or set to reasonable default values. The following arguments are defined:
:processprocess:namename:bufferbuffer:portport- Any of these arguments can be given to identify the process that is to be configured. If none of these arguments is given, the current buffer's process is used.
:speedspeed- The speed of the serial port in bits per second, a.k.a. baud rate. The value can be any number, but most serial ports work only at a few defined values between 1200 and 115200, with 9600 being the most common value. If speed is
nil, the function ignores all other arguments and does not configure the port. This may be useful for special serial ports such as Bluetooth-to-serial converters which can only be configured through AT commands sent through the connection. The value ofnilfor speed is valid only for connections that were already opened by a previous call tomake-serial-processorserial-term.:bytesizebytesize- The number of bits per byte, which can be 7 or 8. If bytesize is not given or
nil, it defaults to 8.:parityparity- The value can be
nil(don't use parity), the symbolodd(use odd parity), or the symboleven(use even parity). If parity is not given, it defaults to no parity.:stopbitsstopbits- The number of stopbits used to terminate a transmission of each byte. stopbits can be 1 or 2. If stopbits is not given or
nil, it defaults to 1.:flowcontrolflowcontrol- The type of flow control to use for this connection, which is either
nil(don't use flow control), the symbolhw(use RTS/CTS hardware flow control), or the symbolsw(use XON/XOFF software flow control). If flowcontrol is not given, it defaults to no flow control.
serial-process-configureis called bymake-serial-processfor the initial configuration of the serial port.Examples:
(serial-process-configure :process "/dev/ttyS0" :speed 1200) (serial-process-configure :buffer "COM1" :stopbits 1 :parity 'odd :flowcontrol 'hw) (serial-process-configure :port "\\\\.\\COM13" :bytesize 7)
This section describes how to pack and unpack arrays of bytes, usually for binary network protocols. These functions convert byte arrays to alists, and vice versa. The byte array can be represented as a unibyte string or as a vector of integers, while the alist associates symbols either with fixed-size objects or with recursive sub-alists.
Conversion from byte arrays to nested alists is also known as deserializing or unpacking, while going in the opposite direction is also known as serializing or packing.
To control unpacking and packing, you write a data layout specification, a special nested list describing named and typed fields. This specification controls length of each field to be processed, and how to pack or unpack it. We normally keep bindat specs in variables whose names end in ‘-bindat-spec’; that kind of name is automatically recognized as “risky.”
A field's type describes the size (in bytes) of the object
that the field represents and, in the case of multibyte fields, how
the bytes are ordered within the field. The two possible orderings
are “big endian” (also known as “network byte ordering”) and
“little endian.” For instance, the number #x23cd (decimal
9165) in big endian would be the two bytes #x23 #xcd;
and in little endian, #xcd #x23. Here are the possible
type values:
u8byteu16wordshortu24u32dwordlongu16ru24ru32rstr lenstrz lenvec len [type](vec len [type]).
ip[127 0 0 1] for localhost.
bits len8 *
len − 1 and ending with zero. For example: bits
2 unpacks #x28 #x1c to (2 3 4 11 13) and
#x1c #x28 to (3 5 10 11 12).
(eval form)For a fixed-size field, the length len is given as an integer specifying the number of bytes in the field.
When the length of a field is not fixed, it typically depends on the
value of a preceding field. In this case, the length len can be
given either as a list (name ...) identifying a
field name in the format specified for bindat-get-field
below, or by an expression (eval form) where form
should evaluate to an integer, specifying the field length.
A field specification generally has the form ([name]
handler). The square braces indicate that name is
optional. (Don't use names that are symbols meaningful as type
specifications (above) or handler specifications (below), since that
would be ambiguous.) name can be a symbol or the expression
(eval form), in which case form should evaluate to
a symbol.
handler describes how to unpack or pack the field and can be one of the following:
eval formfill lenalign lenstruct spec-nameunion form (tag spec)...(eval expr), evaluate
expr with the variable tag dynamically bound to the value
of form. A non-nil result indicates a match.
equal to the value of form.
t.
repeat count field-specs...eval form is used, it is evaluated just once.
For correct operation, each spec in field-specs must include a name.
For the (eval form) forms used in a bindat specification,
the form can access and update these dynamically bound variables
during evaluation:
lastbindat-rawbindat-idxbindat-raw) for unpacking or packing.
structbindat-get-field to access specific fields of this structure.
countindexrepeat block, these contain the maximum number of
repetitions (as specified by the count parameter), and the
current repetition number (counting from 0). Setting count to
zero will terminate the inner-most repeat block after the current
repetition has completed.
In the following documentation, spec refers to a data layout
specification, bindat-raw to a byte array, and struct to an
alist representing unpacked field data.
This function unpacks data from the unibyte string or byte array
bindat-rawaccording to spec. Normally this starts unpacking at the beginning of the byte array, but if bindat-idx is non-nil, it specifies a zero-based starting position to use instead.The value is an alist or nested alist in which each element describes one unpacked field.
This function selects a field's data from the nested alist struct. Usually struct was returned by
bindat-unpack. If name corresponds to just one argument, that means to extract a top-level field value. Multiple name arguments specify repeated lookup of sub-structures. An integer name acts as an array index.For example, if name is
(a b 2 c), that means to find fieldcin the third element of subfieldbof fielda. (This corresponds tostruct.a.b[2].cin C.)
Although packing and unpacking operations change the organization of data (in memory), they preserve the data's total length, which is the sum of all the fields' lengths, in bytes. This value is not generally inherent in either the specification or alist alone; instead, both pieces of information contribute to its calculation. Likewise, the length of a string or array being unpacked may be longer than the data's total length as described by the specification.
This function returns the total length of the data in struct, according to spec.
This function returns a byte array packed according to spec from the data in the alist struct. Normally it creates and fills a new byte array starting at the beginning. However, if bindat-raw is non-
nil, it specifies a pre-allocated unibyte string or vector to pack into. If bindat-idx is non-nil, it specifies the starting offset for packing intobindat-raw.When pre-allocating, you should make sure
(lengthbindat-raw)meets or exceeds the total length to avoid an out-of-range error.
Convert the Internet address vector ip to a string in the usual dotted notation.
(bindat-ip-to-string [127 0 0 1]) ⇒ "127.0.0.1"
Here is a complete example of byte unpacking and packing:
(defvar fcookie-index-spec
'((:version u32)
(:count u32)
(:longest u32)
(:shortest u32)
(:flags u32)
(:delim u8)
(:ignored fill 3)
(:offset repeat (:count)
(:foo u32)))
"Description of a fortune cookie index file's contents.")
(defun fcookie (cookies &optional index)
"Display a random fortune cookie from file COOKIES.
Optional second arg INDEX specifies the associated index
filename, which is by default constructed by appending
\".dat\" to COOKIES. Display cookie text in possibly
new buffer \"*Fortune Cookie: BASENAME*\" where BASENAME
is COOKIES without the directory part."
(interactive "fCookies file: ")
(let* ((info (with-temp-buffer
(insert-file-contents-literally
(or index (concat cookies ".dat")))
(bindat-unpack fcookie-index-spec
(buffer-string))))
(sel (random (bindat-get-field info :count)))
(beg (cdar (bindat-get-field info :offset sel)))
(end (or (cdar (bindat-get-field info
:offset (1+ sel)))
(nth 7 (file-attributes cookies)))))
(switch-to-buffer
(get-buffer-create
(format "*Fortune Cookie: %s*"
(file-name-nondirectory cookies))))
(erase-buffer)
(insert-file-contents-literally
cookies nil beg (- end 3))))
(defun fcookie-create-index (cookies &optional index delim)
"Scan file COOKIES, and write out its index file.
Optional second arg INDEX specifies the index filename,
which is by default constructed by appending \".dat\" to
COOKIES. Optional third arg DELIM specifies the unibyte
character which, when found on a line of its own in
COOKIES, indicates the border between entries."
(interactive "fCookies file: ")
(setq delim (or delim ?%))
(let ((delim-line (format "\n%c\n" delim))
(count 0)
(max 0)
min p q len offsets)
(unless (= 3 (string-bytes delim-line))
(error "Delimiter cannot be represented in one byte"))
(with-temp-buffer
(insert-file-contents-literally cookies)
(while (and (setq p (point))
(search-forward delim-line (point-max) t)
(setq len (- (point) 3 p)))
(setq count (1+ count)
max (max max len)
min (min (or min max) len)
offsets (cons (1- p) offsets))))
(with-temp-buffer
(set-buffer-multibyte nil)
(insert
(bindat-pack
fcookie-index-spec
`((:version . 2)
(:count . ,count)
(:longest . ,max)
(:shortest . ,min)
(:flags . 0)
(:delim . ,delim)
(:offset . ,(mapcar (lambda (o)
(list (cons :foo o)))
(nreverse offsets))))))
(let ((coding-system-for-write 'raw-text-unix))
(write-file (or index (concat cookies ".dat")))))))
Following is an example of defining and unpacking a complex structure. Consider the following C structures:
struct header {
unsigned long dest_ip;
unsigned long src_ip;
unsigned short dest_port;
unsigned short src_port;
};
struct data {
unsigned char type;
unsigned char opcode;
unsigned short length; /* In network byte order */
unsigned char id[8]; /* null-terminated string */
unsigned char data[/* (length + 3) & ~3 */];
};
struct packet {
struct header header;
unsigned long counters[2]; /* In little endian order */
unsigned char items;
unsigned char filler[3];
struct data item[/* items */];
};
The corresponding data layout specification:
(setq header-spec
'((dest-ip ip)
(src-ip ip)
(dest-port u16)
(src-port u16)))
(setq data-spec
'((type u8)
(opcode u8)
(length u16) ;; network byte order
(id strz 8)
(data vec (length))
(align 4)))
(setq packet-spec
'((header struct header-spec)
(counters vec 2 u32r) ;; little endian order
(items u8)
(fill 3)
(item repeat (items)
(struct data-spec))))
A binary data representation:
(setq binary-data
[ 192 168 1 100 192 168 1 101 01 28 21 32
160 134 1 0 5 1 0 0 2 0 0 0
2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])
The corresponding decoded structure:
(setq decoded (bindat-unpack packet-spec binary-data))
⇒
((header
(dest-ip . [192 168 1 100])
(src-ip . [192 168 1 101])
(dest-port . 284)
(src-port . 5408))
(counters . [100000 261])
(items . 2)
(item ((data . [1 2 3 4 5])
(id . "ABCDEF")
(length . 5)
(opcode . 3)
(type . 2))
((data . [6 7 8 9 10 11 12])
(id . "BCDEFG")
(length . 7)
(opcode . 4)
(type . 1))))
Fetching data from this structure:
(bindat-get-field decoded 'item 1 'id)
⇒ "BCDEFG"
This chapter describes a number of features related to the display that Emacs presents to the user.
The function redraw-frame clears and redisplays the entire
contents of a given frame (see Frames). This is useful if the
screen is corrupted.
Even more powerful is redraw-display:
In Emacs, processing user input takes priority over redisplay. If you call these functions when input is available, they don't redisplay immediately, but the requested redisplay does happen eventually—after all the input has been processed.
On text-only terminals, suspending and resuming Emacs normally also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption.
This variable controls whether Emacs redraws the entire screen after it has been suspended and resumed. Non-
nilmeans there is no need to redraw,nilmeans redrawing is needed. The default isnil.
Emacs normally tries to redisplay the screen whenever it waits for input. With the following function, you can request an immediate attempt to redisplay, in the middle of Lisp code, without actually waiting for input.
This function tries immediately to redisplay, provided there are no pending input events.
If the optional argument force is non-
nil, it does all pending redisplay work even if input is available, with no pre-emption.The function returns
tif it actually tried to redisplay, andnilotherwise. A value oftdoes not mean that redisplay proceeded to completion; it could have been pre-empted by newly arriving terminal input.
redisplay with no argument tries immediately to redisplay,
but has no effect on the usual rules for what parts of the screen to
redisplay. By contrast, the following function adds certain windows
to the pending redisplay work (as if their contents had completely
changed), but doesn't immediately try to do any redisplay work.
This function forces some or all windows to be updated on next redisplay. If object is a window, it requires eventual redisplay of that window. If object is a buffer or buffer name, it requires eventual redisplay of all windows displaying that buffer. If object is
nil(or omitted), it requires eventual redisplay of all windows.
force-window-update does not do a redisplay immediately.
(Emacs will do that when it waits for input.) Rather, its effect is
to put more work on the queue to be done by redisplay whenever there
is a chance.
Emacs redisplay normally stops if input arrives, and does not happen
at all if input is available before it starts. Most of the time, this
is exactly what you want. However, you can prevent preemption by
binding redisplay-dont-pause to a non-nil value.
If this variable is non-
nil, pending input does not prevent or halt redisplay; redisplay occurs, and finishes, regardless of whether input is available.
This variable specifies how many seconds Emacs waits between checks for new input during redisplay. (The default is 0.1 seconds.) If input has arrived when Emacs checks, it pre-empts redisplay and processes the available input before trying again to redisplay.
If this variable is
nil, Emacs does not check for input during redisplay, and redisplay cannot be preempted by input.This variable is only obeyed on graphical terminals. For text terminals, see Terminal Output.
When a line of text extends beyond the right edge of a window, Emacs can continue the line (make it “wrap” to the next screen line), or truncate the line (limit it to one screen line). The additional screen lines used to display a long text line are called continuation lines. Continuation is not the same as filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. See Filling.
On a graphical display, tiny arrow images in the window fringes indicate truncated and continued lines (see Fringes). On a text terminal, a ‘$’ in the rightmost column of the window indicates truncation; a ‘\’ on the rightmost column indicates a line that “wraps.” (The display table can specify alternate characters to use for this; see Display Tables).
If this buffer-local variable is non-
nil, lines that extend beyond the right edge of the window are truncated; otherwise, they are continued. As a special exception, the variabletruncate-partial-width-windowstakes precedence in partial-width windows (i.e., windows that do not occupy the entire frame width).
This variable controls line truncation in partial-width windows. A partial-width window is one that does not occupy the entire frame width (see Splitting Windows). If the value is
nil, line truncation is determined by the variabletruncate-lines(see above). If the value is an integer n, lines are truncated if the partial-width window has fewer than n columns, regardless of the value oftruncate-lines; if the partial-width window has n or more columns, line truncation is determined bytruncate-lines. For any other non-nilvalue, lines are truncated in every partial-width window, regardless of the value oftruncate-lines.
When horizontal scrolling (see Horizontal Scrolling) is in use in a window, that forces truncation.
If this buffer-local variable is non-
nil, it defines a “prefix” that is prepended to every continuation line at display-time. (If lines are truncated, the wrap-prefix is never used.) It may be a string, an image, or a stretch-glyph; the value is interpreted in the same way as adisplaytext property. See Display Property.A wrap-prefix may also be specified for regions of text, using the
wrap-prefixtext or overlay property. This takes precedence over thewrap-prefixvariable. See Special Properties.
If this buffer-local variable is non-
nil, it defines a “prefix” that is prepended to every non-continuation line at display-time. It may be a string, an image, or a stretch-glyph; the value is interpreted in the same way as adisplaytext property. See Display Property.A line-prefix may also be specified for regions of text using the
line-prefixtext or overlay property. This takes precedence over theline-prefixvariable. See Special Properties.
If your buffer contains very long lines, and you use
continuation to display them, computing the continuation lines can
make Emacs redisplay slow. The column computation and indentation
functions also become slow. Then you might find it advisable to set
cache-long-line-scans to t.
If this variable is non-
nil, various indentation and motion functions, and Emacs redisplay, cache the results of scanning the buffer, and consult the cache to avoid rescanning regions of the buffer unless they are modified.Turning on the cache slows down processing of short lines somewhat.
This variable is automatically buffer-local in every buffer.
The echo area is used for displaying error messages
(see Errors), for messages made with the message primitive,
and for echoing keystrokes. It is not the same as the minibuffer,
despite the fact that the minibuffer appears (when active) in the same
place on the screen as the echo area. The GNU Emacs Manual
specifies the rules for resolving conflicts between the echo area and
the minibuffer for use of that screen space (see The Minibuffer).
You can write output in the echo area by using the Lisp printing
functions with t as the stream (see Output Functions), or
explicitly.
This section describes the functions for explicitly producing echo area messages. Many other Emacs features display messages there, too.
This function displays a message in the echo area. The argument format-string is similar to a C language
printfformat string. Seeformatin Formatting Strings, for the details on the conversion specifications.messagereturns the constructed string.In batch mode,
messageprints the message text on the standard error stream, followed by a newline.If format-string, or strings among the arguments, have
facetext properties, these affect the way the message is displayed.If format-string is
nilor the empty string,messageclears the echo area; if the echo area has been expanded automatically, this brings it back to its normal size. If the minibuffer is active, this brings the minibuffer contents back onto the screen immediately.(message "Minibuffer depth is %d." (minibuffer-depth)) -| Minibuffer depth is 0. ⇒ "Minibuffer depth is 0." ---------- Echo Area ---------- Minibuffer depth is 0. ---------- Echo Area ----------To automatically display a message in the echo area or in a pop-buffer, depending on its size, use
display-message-or-buffer(see below).
This construct displays a message in the echo area temporarily, during the execution of body. It displays message, executes body, then returns the value of the last body form while restoring the previous echo area contents.
This function displays a message like
message, but may display it in a dialog box instead of the echo area. If this function is called in a command that was invoked using the mouse—more precisely, iflast-nonmenu-event(see Command Loop Info) is eithernilor a list—then it uses a dialog box or pop-up menu to display the message. Otherwise, it uses the echo area. (This is the same criterion thaty-or-n-puses to make a similar decision; see Yes-or-No Queries.)You can force use of the mouse or of the echo area by binding
last-nonmenu-eventto a suitable value around the call.
This function displays a message like
message, but uses a dialog box (or a pop-up menu) whenever that is possible. If it is impossible to use a dialog box or pop-up menu, because the terminal does not support them, thenmessage-boxuses the echo area, likemessage.
This function displays the message message, which may be either a string or a buffer. If it is shorter than the maximum height of the echo area, as defined by
max-mini-window-height, it is displayed in the echo area, usingmessage. Otherwise,display-bufferis used to show it in a pop-up buffer.Returns either the string shown in the echo area, or when a pop-up buffer is used, the window used to display it.
If message is a string, then the optional argument buffer-name is the name of the buffer used to display it when a pop-up buffer is used, defaulting to ‘*Message*’. In the case where message is a string and displayed in the echo area, it is not specified whether the contents are inserted into the buffer anyway.
The optional arguments not-this-window and frame are as for
display-buffer, and only used if a buffer is displayed.
This function returns the message currently being displayed in the echo area, or
nilif there is none.
When an operation can take a while to finish, you should inform the user about the progress it makes. This way the user can estimate remaining time and clearly see that Emacs is busy working, not hung.
Functions listed in this section provide simple and efficient way of reporting operation progress. Here is a working example that does nothing useful:
(let ((progress-reporter
(make-progress-reporter "Collecting mana for Emacs..."
0 500)))
(dotimes (k 500)
(sit-for 0.01)
(progress-reporter-update progress-reporter k))
(progress-reporter-done progress-reporter))
This function creates and returns a progress reporter—an object you will use as an argument for all other functions listed here. The idea is to precompute as much data as possible to make progress reporting very fast.
When this progress reporter is subsequently used, it will display message in the echo area, followed by progress percentage. message is treated as a simple string. If you need it to depend on a filename, for instance, use
formatbefore calling this function.min-value and max-value arguments stand for starting and final states of your operation. For instance, if you scan a buffer, they should be the results of
point-minandpoint-maxcorrespondingly. It is required that max-value is greater than min-value. If you create progress reporter when some part of the operation has already been completed, then specify current-value argument. But normally you should omit it or set it tonil—it will default to min-value then.Remaining arguments control the rate of echo area updates. Progress reporter will wait for at least min-change more percents of the operation to be completed before printing next message. min-time specifies the minimum time in seconds to pass between successive prints. It can be fractional. Depending on Emacs and system capabilities, progress reporter may or may not respect this last argument or do it with varying precision. Default value for min-change is 1 (one percent), for min-time—0.2 (seconds.)
This function calls
progress-reporter-update, so the first message is printed immediately.
This function does the main work of reporting progress of your operation. It displays the message of reporter, followed by progress percentage determined by value. If percentage is zero, or close enough according to the min-change and min-time arguments, then it is omitted from the output.
reporter must be the result of a call to
make-progress-reporter. value specifies the current state of your operation and must be between min-value and max-value (inclusive) as passed tomake-progress-reporter. For instance, if you scan a buffer, then value should be the result of a call topoint.This function respects min-change and min-time as passed to
make-progress-reporterand so does not output new messages on every invocation. It is thus very fast and normally you should not try to reduce the number of calls to it: resulting overhead will most likely negate your effort.
This function is similar to
progress-reporter-updateexcept that it prints a message in the echo area unconditionally.The first two arguments have the same meaning as for
progress-reporter-update. Optional new-message allows you to change the message of the reporter. Since this functions always updates the echo area, such a change will be immediately presented to the user.
This function should be called when the operation is finished. It prints the message of reporter followed by word “done” in the echo area.
You should always call this function and not hope for
progress-reporter-updateto print “100%.” Firstly, it may never print it, there are many good reasons for this not to happen. Secondly, “done” is more explicit.
This is a convenience macro that works the same way as
dotimesdoes, but also reports loop progress using the functions described above. It allows you to save some typing.You can rewrite the example in the beginning of this node using this macro this way:
(dotimes-with-progress-reporter (k 500) "Collecting some mana for Emacs..." (sit-for 0.01))
Almost all the messages displayed in the echo area are also recorded
in the ‘*Messages*’ buffer so that the user can refer back to
them. This includes all the messages that are output with
message.
This variable specifies how many lines to keep in the ‘*Messages*’ buffer. The value
tmeans there is no limit on how many lines to keep. The valuenildisables message logging entirely. Here's how to display a message and prevent it from being logged:(let (message-log-max) (message ...))
To make ‘*Messages*’ more convenient for the user, the logging facility combines successive identical messages. It also combines successive related messages for the sake of two cases: question followed by answer, and a series of progress messages.
A “question followed by an answer” means two messages like the
ones produced by y-or-n-p: the first is ‘question’,
and the second is ‘question...answer’. The first
message conveys no additional information beyond what's in the second,
so logging the second message discards the first from the log.
A “series of progress messages” means successive messages like
those produced by make-progress-reporter. They have the form
‘base...how-far’, where base is the same each
time, while how-far varies. Logging each message in the series
discards the previous one, provided they are consecutive.
The functions make-progress-reporter and y-or-n-p
don't have to do anything special to activate the message log
combination feature. It operates whenever two consecutive messages
are logged that share a common prefix ending in ‘...’.
These variables control details of how the echo area works.
This variable controls where the cursor appears when a message is displayed in the echo area. If it is non-
nil, then the cursor appears at the end of the message. Otherwise, the cursor appears at point—not in the echo area at all.The value is normally
nil; Lisp programs bind it totfor brief periods of time.
This normal hook is run whenever the echo area is cleared—either by
(message nil)or for any other reason.
This variable determines how much time should elapse before command characters echo. Its value must be an integer or floating point number, which specifies the number of seconds to wait before echoing. If the user types a prefix key (such as C-x) and then delays this many seconds before continuing, the prefix key is echoed in the echo area. (Once echoing begins in a key sequence, all subsequent characters in the same key sequence are echoed immediately.)
If the value is zero, then command input is not echoed.
Normally, displaying a long message resizes the echo area to display the entire message. But if the variable
message-truncate-linesis non-nil, the echo area does not resize, and the message is truncated to fit it, as in Emacs 20 and before.
The variable max-mini-window-height, which specifies the
maximum height for resizing minibuffer windows, also applies to the
echo area (which is really a special use of the minibuffer window.
See Minibuffer Misc.).
Warnings are a facility for a program to inform the user of a possible problem, but continue running.
Every warning has a textual message, which explains the problem for the user, and a severity level which is a symbol. Here are the possible severity levels, in order of decreasing severity, and their meanings:
:emergency:error:warning:debugWhen your program encounters invalid input data, it can either
signal a Lisp error by calling error or signal or report
a warning with severity :error. Signaling a Lisp error is the
easiest thing to do, but it means the program cannot continue
processing. If you want to take the trouble to implement a way to
continue processing despite the bad data, then reporting a warning of
severity :error is the right way to inform the user of the
problem. For instance, the Emacs Lisp byte compiler can report an
error that way and continue compiling other functions. (If the
program signals a Lisp error and then handles it with
condition-case, the user won't see the error message; it could
show the message to the user by reporting it as a warning.)
Each warning has a warning type to classify it. The type is a
list of symbols. The first symbol should be the custom group that you
use for the program's user options. For example, byte compiler
warnings use the warning type (bytecomp). You can also
subcategorize the warnings, if you wish, by using more symbols in the
list.
This function reports a warning, using message as the message and type as the warning type. level should be the severity level, with
:warningbeing the default.buffer-name, if non-
nil, specifies the name of the buffer for logging the warning. By default, it is ‘*Warnings*’.
This function reports a warning using the value of
(formatmessage args...)as the message. In other respects it is equivalent todisplay-warning.
This function reports a warning using the value of
(formatmessage args...)as the message,(emacs)as the type, and:warningas the severity level. It exists for compatibility only; we recommend not using it, because you should specify a specific warning type.
Programs can customize how their warnings appear by binding the variables described in this section.
This list defines the meaning and severity order of the warning severity levels. Each element defines one severity level, and they are arranged in order of decreasing severity.
Each element has the form
(level string function), where level is the severity level it defines. string specifies the textual description of this level. string should use ‘%s’ to specify where to put the warning type information, or it can omit the ‘%s’ so as not to include that information.The optional function, if non-
nil, is a function to call with no arguments, to get the user's attention.Normally you should not change the value of this variable.
If non-
nil, the value is a function to generate prefix text for warnings. Programs can bind the variable to a suitable function.display-warningcalls this function with the warnings buffer current, and the function can insert text in it. That text becomes the beginning of the warning message.The function is called with two arguments, the severity level and its entry in
warning-levels. It should return a list to use as the entry (this value need not be an actual member ofwarning-levels). By constructing this value, the function can change the severity of the warning, or specify different handling for a given severity level.If the variable's value is
nilthen there is no function to call.
Programs can bind this variable to
tto say that the next warning should begin a series. When several warnings form a series, that means to leave point on the first warning of the series, rather than keep moving it for each warning so that it appears on the last one. The series ends when the local binding is unbound andwarning-seriesbecomesnilagain.The value can also be a symbol with a function definition. That is equivalent to
t, except that the next warning will also call the function with no arguments with the warnings buffer current. The function can insert text which will serve as a header for the series of warnings.Once a series has begun, the value is a marker which points to the buffer position in the warnings buffer of the start of the series.
The variable's normal value is
nil, which means to handle each warning separately.
When this variable is non-
nil, it specifies a fill prefix to use for filling each warning's text.
This variable specifies the format for displaying the warning type in the warning message. The result of formatting the type this way gets included in the message under the control of the string in the entry in
warning-levels. The default value is" (%s)". If you bind it to""then the warning type won't appear at all.
These variables are used by users to control what happens when a Lisp program reports a warning.
This user option specifies the minimum severity level that should be shown immediately to the user. The default is
:warning, which means to immediately display all warnings except:debugwarnings.
This user option specifies the minimum severity level that should be logged in the warnings buffer. The default is
:warning, which means to log all warnings except:debugwarnings.
This list specifies which warning types should not be displayed immediately for the user. Each element of the list should be a list of symbols. If its elements match the first elements in a warning type, then that warning is not displayed immediately.
This list specifies which warning types should not be logged in the warnings buffer. Each element of the list should be a list of symbols. If it matches the first few elements in a warning type, then that warning is not logged.
You can make characters invisible, so that they do not appear on
the screen, with the invisible property. This can be either a
text property (see Text Properties) or a property of an overlay
(see Overlays). Cursor motion also partly ignores these
characters; if the command loop finds point within them, it moves
point to the other side of them.
In the simplest case, any non-nil invisible property makes
a character invisible. This is the default case—if you don't alter
the default value of buffer-invisibility-spec, this is how the
invisible property works. You should normally use t
as the value of the invisible property if you don't plan
to set buffer-invisibility-spec yourself.
More generally, you can use the variable buffer-invisibility-spec
to control which values of the invisible property make text
invisible. This permits you to classify the text into different subsets
in advance, by giving them different invisible values, and
subsequently make various subsets visible or invisible by changing the
value of buffer-invisibility-spec.
Controlling visibility with buffer-invisibility-spec is
especially useful in a program to display the list of entries in a
database. It permits the implementation of convenient filtering
commands to view just a part of the entries in the database. Setting
this variable is very fast, much faster than scanning all the text in
the buffer looking for properties to change.
This variable specifies which kinds of
invisibleproperties actually make a character invisible. Setting this variable makes it buffer-local.
t- A character is invisible if its
invisibleproperty is non-nil. This is the default.- a list
- Each element of the list specifies a criterion for invisibility; if a character's
invisibleproperty fits any one of these criteria, the character is invisible. The list can have two kinds of elements:
- atom
- A character is invisible if its
invisibleproperty value is atom or if it is a list with atom as a member.(atom. t)- A character is invisible if its
invisibleproperty value is atom or if it is a list with atom as a member. Moreover, a sequence of such characters displays as an ellipsis.
Two functions are specifically provided for adding elements to
buffer-invisibility-spec and removing elements from it.
This function adds the element element to
buffer-invisibility-spec. Ifbuffer-invisibility-specwast, it changes to a list,(t), so that text whoseinvisibleproperty istremains invisible.
This removes the element element from
buffer-invisibility-spec. This does nothing if element is not in the list.
A convention for use of buffer-invisibility-spec is that a
major mode should use the mode's own name as an element of
buffer-invisibility-spec and as the value of the
invisible property:
;; If you want to display an ellipsis: (add-to-invisibility-spec '(my-symbol . t)) ;; If you don't want ellipsis: (add-to-invisibility-spec 'my-symbol) (overlay-put (make-overlay beginning end) 'invisible 'my-symbol) ;; When done with the overlays: (remove-from-invisibility-spec '(my-symbol . t)) ;; Or respectively: (remove-from-invisibility-spec 'my-symbol)
You can check for invisibility using the following function:
If pos-or-prop is a marker or number, this function returns a non-
nilvalue if the text at that position is invisible.If pos-or-prop is any other kind of Lisp object, that is taken to mean a possible value of the
invisibletext or overlay property. In that case, this function returns a non-nilvalue if that value would cause text to become invisible, based on the current value ofbuffer-invisibility-spec.
Ordinarily, functions that operate on text or move point do not care
whether the text is invisible. The user-level line motion commands
ignore invisible newlines if line-move-ignore-invisible is
non-nil (the default), but only because they are explicitly
programmed to do so.
However, if a command ends with point inside or immediately before invisible text, the main editing loop moves point further forward or further backward (in the same direction that the command already moved it) until that condition is no longer true. Thus, if the command moved point back into an invisible range, Emacs moves point back to the beginning of that range, and then back one more character. If the command moved point forward into an invisible range, Emacs moves point forward up to the first visible character that follows the invisible text.
Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text. To enable
this, the overlay should have a non-nil
isearch-open-invisible property. The property value should be a
function to be called with the overlay as an argument. This function
should make the overlay visible permanently; it is used when the match
overlaps the overlay on exit from the search.
During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties. If you
want this to be done differently for a certain overlay, give it an
isearch-open-invisible-temporary property which is a function.
The function is called with two arguments: the first is the overlay, and
the second is nil to make the overlay visible, or t to
make it invisible again.
Selective display refers to a pair of related features for hiding certain lines on the screen.
The first variant, explicit selective display, is designed for use
in a Lisp program: it controls which lines are hidden by altering the
text. This kind of hiding in some ways resembles the effect of the
invisible property (see Invisible Text), but the two
features are different and do not work the same way.
In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be a user-level feature.
The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text that was formerly a line following that newline is now hidden. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For
example, C-f (forward-char) moves point unhesitatingly
into hidden text. However, the replacement of newline characters with
carriage return characters affects some editing commands. For
example, next-line skips hidden lines, since it searches only
for newlines. Modes that use selective display can also define
commands that take account of the newlines, or that control which
parts of the text are hidden.
When you write a selectively displayed buffer into a file, all the control-m's are output as newlines. This means that when you next read in the file, it looks OK, with nothing hidden. The selective display effect is seen only within Emacs.
This buffer-local variable enables selective display. This means that lines, or portions of lines, may be made hidden.
- If the value of
selective-displayist, then the character control-m marks the start of hidden text; the control-m, and the rest of the line following it, are not displayed. This is explicit selective display.- If the value of
selective-displayis a positive integer, then lines that start with more than that many columns of indentation are not displayed.When some portion of a buffer is hidden, the vertical movement commands operate as if that portion did not exist, allowing a single
next-linecommand to skip any number of hidden lines. However, character movement commands (such asforward-char) do not skip the hidden portion, and it is possible (if tricky) to insert or delete text in an hidden portion.In the examples below, we show the display appearance of the buffer
foo, which changes with the value ofselective-display. The contents of the buffer do not change.(setq selective-display nil) ⇒ nil ---------- Buffer: foo ---------- 1 on this column 2on this column 3n this column 3n this column 2on this column 1 on this column ---------- Buffer: foo ---------- (setq selective-display 2) ⇒ 2 ---------- Buffer: foo ---------- 1 on this column 2on this column 2on this column 1 on this column ---------- Buffer: foo ----------
If this buffer-local variable is non-
nil, then Emacs displays ‘...’ at the end of a line that is followed by hidden text. This example is a continuation of the previous one.(setq selective-display-ellipses t) ⇒ t ---------- Buffer: foo ---------- 1 on this column 2on this column ... 2on this column 1 on this column ---------- Buffer: foo ----------You can use a display table to substitute other text for the ellipsis (‘...’). See Display Tables.
Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature.
This function executes forms while arranging to insert any output they print into the buffer named buffer-name, which is first created if necessary, and put into Help mode. Finally, the buffer is displayed in some window, but not selected.
If the forms do not change the major mode in the output buffer, so that it is still Help mode at the end of their execution, then
with-output-to-temp-buffermakes this buffer read-only at the end, and also scans it for function and variable names to make them into clickable cross-references. See Tips for Documentation Strings, in particular the item on hyperlinks in documentation strings, for more details.The string buffer-name specifies the temporary buffer, which need not already exist. The argument must be a string, not a buffer. The buffer is erased initially (with no questions asked), and it is marked as unmodified after
with-output-to-temp-bufferexits.
with-output-to-temp-bufferbindsstandard-outputto the temporary buffer, then it evaluates the forms in forms. Output using the Lisp output functions within forms goes by default to that buffer (but screen display and messages in the echo area, although they are “output” in the general sense of the word, are not affected). See Output Functions.Several hooks are available for customizing the behavior of this construct; they are listed below.
The value of the last form in forms is returned.
---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ---------- (with-output-to-temp-buffer "foo" (print 20) (print standard-output)) ⇒ #<buffer foo> ---------- Buffer: foo ---------- 20 #<buffer foo> ---------- Buffer: foo ----------
If this variable is non-
nil,with-output-to-temp-buffercalls it as a function to do the job of displaying a help buffer. The function gets one argument, which is the buffer it should display.It is a good idea for this function to run
temp-buffer-show-hookjust aswith-output-to-temp-buffernormally would, inside ofsave-selected-windowand with the chosen window and buffer selected.
This normal hook is run by
with-output-to-temp-bufferbefore evaluating body. When the hook runs, the temporary buffer is current. This hook is normally set up with a function to put the buffer in Help mode.
This normal hook is run by
with-output-to-temp-bufferafter displaying the temporary buffer. When the hook runs, the temporary buffer is current, and the window it was displayed in is selected.
This function momentarily displays string in the current buffer at position. It has no effect on the undo list or on the buffer's modification status.
The momentary display remains until the next input event. If the next input event is char,
momentary-string-displayignores it and returns. Otherwise, that event remains buffered for subsequent use as input. Thus, typing char will simply remove the string from the display, while typing (say) C-f will remove the string from the display and later (presumably) move point forward. The argument char is a space by default.The return value of
momentary-string-displayis not meaningful.If the string string does not contain control characters, you can do the same job in a more general way by creating (and then subsequently deleting) an overlay with a
before-stringproperty. See Overlay Properties.If message is non-
nil, it is displayed in the echo area while string is displayed in the buffer. If it isnil, a default message says to type char to continue.In this example, point is initially located at the beginning of the second line:
---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") ⇒ t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------
You can use overlays to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay.
The visual effect of an overlay is the same as of the corresponding text property (see Text Properties). However, due to a different implementation, overlays generally don't scale well (many operations take a time that is proportional to the number of overlays in the buffer). If you need to affect the visual appearance of many portions in the buffer, we recommend using text properties.
An overlay uses markers to record its beginning and end; thus, editing the text of the buffer adjusts the beginning and end of each overlay so that it stays with the text. When you create the overlay, you can specify whether text inserted at the beginning should be inside the overlay or outside, and likewise for the end of the overlay.
This section describes the functions to create, delete and move overlays, and to examine their contents. Overlay changes are not recorded in the buffer's undo list, since the overlays are not part of the buffer's contents.
This function creates and returns an overlay that belongs to buffer and ranges from start to end. Both start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay is created in the current buffer.
The arguments front-advance and rear-advance specify the marker insertion type for the start of the overlay and for the end of the overlay, respectively. See Marker Insertion Types. If they are both
nil, the default, then the overlay extends to include any text inserted at the beginning, but not text inserted at the end. If front-advance is non-nil, text inserted at the beginning of the overlay is excluded from the overlay. If rear-advance is non-nil, text inserted at the end of the overlay is included in the overlay.
This function returns the position at which overlay starts, as an integer.
This function returns the position at which overlay ends, as an integer.
This function returns the buffer that overlay belongs to. It returns
nilif overlay has been deleted.
This function deletes overlay. The overlay continues to exist as a Lisp object, and its property list is unchanged, but it ceases to be attached to the buffer it belonged to, and ceases to have any effect on display.
A deleted overlay is not permanently disconnected. You can give it a position in a buffer again by calling
move-overlay.
This function moves overlay to buffer, and places its bounds at start and end. Both arguments start and end must specify buffer positions; they may be integers or markers.
If buffer is omitted, overlay stays in the same buffer it was already associated with; if overlay was deleted, it goes into the current buffer.
The return value is overlay.
This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be “lost.”
This function removes all the overlays between start and end whose property name has the value value. It can move the endpoints of the overlays in the region, or split them.
If name is omitted or
nil, it means to delete all overlays in the specified region. If start and/or end are omitted ornil, that means the beginning and end of the buffer respectively. Therefore,(remove-overlays)removes all the overlays in the current buffer.
This function returns a copy of overlay. The copy has the same endpoints and properties as overlay. However, the marker insertion type for the start of the overlay and for the end of the overlay are set to their default values (see Marker Insertion Types).
Here are some examples:
;; Create an overlay. (setq foo (make-overlay 1 10)) ⇒ #<overlay from 1 to 10 in display.texi> (overlay-start foo) ⇒ 1 (overlay-end foo) ⇒ 10 (overlay-buffer foo) ⇒ #<buffer display.texi> ;; Give it a property we can check later. (overlay-put foo 'happy t) ⇒ t ;; Verify the property is present. (overlay-get foo 'happy) ⇒ t ;; Move the overlay. (move-overlay foo 5 20) ⇒ #<overlay from 5 to 20 in display.texi> (overlay-start foo) ⇒ 5 (overlay-end foo) ⇒ 20 ;; Delete the overlay. (delete-overlay foo) ⇒ nil ;; Verify it is deleted. foo ⇒ #<overlay in no buffer> ;; A deleted overlay has no position. (overlay-start foo) ⇒ nil (overlay-end foo) ⇒ nil (overlay-buffer foo) ⇒ nil ;; Undelete the overlay. (move-overlay foo 1 20) ⇒ #<overlay from 1 to 20 in display.texi> ;; Verify the results. (overlay-start foo) ⇒ 1 (overlay-end foo) ⇒ 20 (overlay-buffer foo) ⇒ #<buffer display.texi> ;; Moving and deleting the overlay does not change its properties. (overlay-get foo 'happy) ⇒ t
Emacs stores the overlays of each buffer in two lists, divided around an arbitrary “center position.” One list extends backwards through the buffer from that center position, and the other extends forwards from that center position. The center position can be anywhere in the buffer.
This function recenters the overlays of the current buffer around position pos. That makes overlay lookup faster for positions near pos, but slower for positions far away from pos.
A loop that scans the buffer forwards, creating overlays, can run
faster if you do (overlay-recenter (point-max)) first.
Overlay properties are like text properties in that the properties that alter how a character is displayed can come from either source. But in most respects they are different. See Text Properties, for comparison.
Text properties are considered a part of the text; overlays and their properties are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text property changes, overlay property changes are not recorded in the buffer's undo list.
Since more than one overlay can specify a property value for the same character, Emacs lets you specify a priority value of each overlay. You should not make assumptions about which overlay will prevail when there is a conflict and they have the same priority.
These functions read and set the properties of an overlay:
This function returns the value of property prop recorded in overlay, if any. If overlay does not record any value for that property, but it does have a
categoryproperty which is a symbol, that symbol's prop property is used. Otherwise, the value isnil.
This function sets the value of property prop recorded in overlay to value. It returns value.
See also the function get-char-property which checks both
overlay properties and text properties for a given character.
See Examining Properties.
Many overlay properties have special meanings; here is a table of them:
prioritynil,
means zero.
The priority matters when two or more overlays cover the same
character and both specify the same property; the one whose
priority value is larger overrides the other. For the
face property, the higher priority overlay's value does not
completely override the other value; instead, its face attributes
override the face attributes of the lower priority face
property.
Currently, all overlays take priority over text properties. Please
avoid using negative priority values, as we have not yet decided just
what they should mean.
windowwindow property is non-nil, then the overlay
applies only on that window.
categorycategory property, we call it the
category of the overlay. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the overlay.
faceIn the simplest case, the value is a face name. It can also be a list; then each element can be any of these possibilities:
(foreground-color . color-name) or
(background-color . color-name). These elements specify
just the foreground color or just the background color.
(foreground-color . color-name) has the same effect as
(:foreground color-name); likewise for the background.
mouse-faceface when the mouse is within
the range of the overlay.
displayhelp-echohelp-echo property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string in the
echo area, or in the tooltip window. For details see Text help-echo.
modification-hooksThe hook functions are called both before and after each change. If the functions save the information they receive, and compare notes between calls, they can determine exactly what change has been made in the buffer text.
When called before a change, each function receives four arguments: the
overlay, nil, and the beginning and end of the text range to be
modified.
When called after a change, each function receives five arguments: the
overlay, t, the beginning and end of the text range just
modified, and the length of the pre-change text replaced by that range.
(For an insertion, the pre-change length is zero; for a deletion, that
length is the number of characters deleted, and the post-change
beginning and end are equal.)
If these functions modify the buffer, they should bind
inhibit-modification-hooks to t around doing so, to
avoid confusing the internal mechanism that calls these hooks.
Text properties also support the modification-hooks property,
but the details are somewhat different (see Special Properties).
insert-in-front-hooksmodification-hooks functions.
insert-behind-hooksmodification-hooks functions.
invisibleinvisible property can make the text in the overlay
invisible, which means that it does not appear on the screen.
See Invisible Text, for details.
intangibleintangible property on an overlay works just like the
intangible text property. See Special Properties, for details.
isearch-open-invisibleisearch-open-invisible-temporarybefore-stringafter-stringline-prefixwrap-prefixevaporatenil, the overlay is deleted automatically
if it becomes empty (i.e., if its length becomes zero). If you give
an empty overlay a non-nil evaporate property, that deletes
it immediately.
local-mapnil, it specifies a keymap for a portion
of the text. The property's value replaces the buffer's local map, when
the character after point is within the overlay. See Active Keymaps.
keymapkeymap property is similar to local-map but overrides the
buffer's local map (and the map specified by the local-map
property) rather than replacing it.
The local-map and keymap properties do not affect a
string displayed by the before-string, after-string, or
display properties. This is only relevant for mouse clicks and
other mouse events that fall on the string, since point is never on
the string. To bind special mouse events for the string, assign it a
local-map or keymap text property. See Special Properties.
This function returns a list of all the overlays that cover the character at position pos in the current buffer. The list is in no particular order. An overlay contains position pos if it begins at or before pos, and ends after pos.
To illustrate usage, here is a Lisp function that returns a list of the overlays that specify property prop for the character at point:
(defun find-overlays-specifying (prop) (let ((overlays (overlays-at (point))) found) (while overlays (let ((overlay (car overlays))) (if (overlay-get overlay prop) (setq found (cons overlay found)))) (setq overlays (cdr overlays))) found))
This function returns a list of the overlays that overlap the region beg through end. “Overlap” means that at least one character is contained within the overlay and also contained within the specified region; however, empty overlays are included in the result if they are located at beg, strictly between beg and end, or at end when end denotes the position at the end of the buffer.
This function returns the buffer position of the next beginning or end of an overlay, after pos. If there is none, it returns
(point-max).
This function returns the buffer position of the previous beginning or end of an overlay, before pos. If there is none, it returns
(point-min).
As an example, here's a simplified (and inefficient) version of the
primitive function next-single-char-property-change
(see Property Search). It searches forward from position
pos for the next position where the value of a given property
prop, as obtained from either overlays or text properties,
changes.
(defun next-single-char-property-change (position prop)
(save-excursion
(goto-char position)
(let ((propval (get-char-property (point) prop)))
(while (and (not (eobp))
(eq (get-char-property (point) prop) propval))
(goto-char (min (next-overlay-change (point))
(next-single-property-change (point) prop)))))
(point)))
Since not all characters have the same width, these functions let you check the width of a character. See Primitive Indent, and Screen Lines, for related functions.
This function returns the width in columns of the character char, if it were displayed in the current buffer and the selected window.
This function returns the width in columns of the string string, if it were displayed in the current buffer and the selected window.
This function returns the part of string that fits within width columns, as a new string.
If string does not reach width, then the result ends where string ends. If one multi-column character in string extends across the column width, that character is not included in the result. Thus, the result can fall short of width but cannot go beyond it.
The optional argument start-column specifies the starting column. If this is non-
nil, then the first start-column columns of the string are omitted from the value. If one multi-column character in string extends across the column start-column, that character is not included.The optional argument padding, if non-
nil, is a padding character added at the beginning and end of the result string, to extend it to exactly width columns. The padding character is used at the end of the result if it falls short of width. It is also used at the beginning of the result if one multi-column character in string extends across the column start-column.If ellipsis is non-
nil, it should be a string which will replace the end of str (including any padding) if it extends beyond end-column, unless the display width of str is equal to or less than the display width of ellipsis. If ellipsis is non-niland not a string, it stands for"...".(truncate-string-to-width "\tab\t" 12 4) ⇒ "ab" (truncate-string-to-width "\tab\t" 12 4 ?\s) ⇒ " ab "
The total height of each display line consists of the height of the contents of the line, plus optional additional vertical line spacing above or below the display line.
The height of the line contents is the maximum height of any character or image on that display line, including the final newline if there is one. (A display line that is continued doesn't include a final newline.) That is the default line height, if you do nothing to specify a greater height. (In the most common case, this equals the height of the default frame font.)
There are several ways to explicitly specify a larger line height, either by specifying an absolute height for the display line, or by specifying vertical space. However, no matter what you specify, the actual line height can never be less than the default.
A newline can have a line-height text or overlay property
that controls the total height of the display line ending in that
newline.
If the property value is t, the newline character has no
effect on the displayed height of the line—the visible contents
alone determine the height. This is useful for tiling small images
(or image slices) without adding blank areas between the images.
If the property value is a list of the form (height
total), that adds extra space below the display line.
First Emacs uses height as a height spec to control extra space
above the line; then it adds enough space below the line
to bring the total line height up to total. In this case, the
other ways to specify the line spacing are ignored.
Any other kind of property value is a height spec, which translates into a number—the specified line height. There are several ways to write a height spec; here's how each of them translates into a number:
(face . ratio)nil which means a ratio of 1.
If face is t, it refers to the current face.
(nil . ratio)Thus, any valid height spec determines the height in pixels, one way or another. If the line contents' height is less than that, Emacs adds extra vertical space above the line to achieve the specified total height.
If you don't specify the line-height property, the line's
height consists of the contents' height plus the line spacing.
There are several ways to specify the line spacing for different
parts of Emacs text.
On graphical terminals, you can specify the line spacing for all
lines in a frame, using the line-spacing frame parameter
(see Layout Parameters). However, if the default value of
line-spacing is non-nil, it overrides the
frame's line-spacing parameter. An integer value specifies the
number of pixels put below lines. A floating point number specifies
the spacing relative to the frame's default line height.
You can specify the line spacing for all lines in a buffer via the
buffer-local line-spacing variable. An integer value specifies
the number of pixels put below lines. A floating point number
specifies the spacing relative to the default frame line height. This
overrides line spacings specified for the frame.
Finally, a newline can have a line-spacing text or overlay
property that overrides the default frame line spacing and the buffer
local line-spacing variable, for the display line ending in
that newline.
One way or another, these mechanisms specify a Lisp value for the spacing of each line. The value is a height spec, and it translates into a Lisp value as described above. However, in this case the numeric height value specifies the line spacing, rather than the line height.
On text-only terminals, the line spacing cannot be altered.
A face is a collection of graphical attributes for displaying text: font family, foreground color, background color, optional underlining, and so on. Faces control how buffer text is displayed, and how some parts of the frame, such as the mode-line, are displayed. See Standard Faces, for the list of faces Emacs normally comes with.
For most purposes, you refer to a face in Lisp programs using its face name. This is either a string or (equivalently) a Lisp symbol whose name is equal to that string.
This function returns a non-
nilvalue if object is a Lisp symbol or string that names a face. Otherwise, it returnsnil.
Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish.
The way to define a new face is with defface. This creates a
kind of customization item (see Customization) which the user can
customize using the Customization buffer (see Easy Customization).
People are sometimes tempted to create variables whose values specify which faces to use (for example, Font-Lock does this). In the vast majority of cases, this is not necessary, and simply using faces directly is preferable.
This declares face as a customizable face whose default attributes are given by spec. You should not quote the symbol face, and it should not end in ‘-face’ (that would be redundant). The argument doc specifies the face documentation. The keywords you can use in
deffaceare the same as indefgroupanddefcustom(see Common Keywords).When
deffaceexecutes, it defines the face according to spec, then uses any customizations that were read from the init file (see Init File) to override that specification.When you evaluate a
deffaceform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunoverrides any customizations of the face. This way, the face reflects exactly what thedeffacesays.The purpose of spec is to specify how the face should appear on different kinds of terminals. It should be an alist whose elements have the form
(display atts). Each element's car, display, specifies a class of terminals. (The first element, if its car isdefault, is special—it specifies defaults for the remaining elements). The element's cadr, atts, is a list of face attributes and their values; it specifies what the face should look like on that kind of terminal. The possible attributes are defined in the value ofcustom-face-attributes.The display part of an element of spec determines which frames the element matches. If more than one element of spec matches a given frame, the first element that matches is the one used for that frame. There are three possibilities for display:
default- This element of spec doesn't match any frames; instead, it specifies defaults that apply to all frames. This kind of element, if used, must be the first element of spec. Each of the following elements can override any or all of these defaults.
t- This element of spec matches all frames. Therefore, any subsequent elements of spec are never used. Normally
tis used in the last (or only) element of spec.- a list
- If display is a list, each element should have the form
(characteristic value...). Here characteristic specifies a way of classifying frames, and the values are possible classifications which display should apply to. Here are the possible values of characteristic:
type- The kind of window system the frame uses—either
graphic(any graphics-capable display),x,pc(for the MS-DOS console),w32(for MS Windows 9X/NT/2K/XP), ortty(a non-graphics-capable display). See window-system.class- What kinds of colors the frame supports—either
color,grayscale, ormono.background- The kind of background—either
lightordark.min-colors- An integer that represents the minimum number of colors the frame should support. This matches a frame if its
display-color-cellsvalue is at least the specified integer.supports- Whether or not the frame can display the face attributes given in value... (see Face Attributes). See Display Face Attribute Testing, for more information on exactly how this testing is done.
If an element of display specifies more than one value for a given characteristic, any of those values is acceptable. If display has more than one element, each element should specify a different characteristic; then each characteristic of the frame must match one of the values specified for it in display.
Here's how the standard face region is defined:
(defface region
'((((class color) (min-colors 88) (background dark))
:background "blue3")
(((class color) (min-colors 88) (background light))
:background "lightgoldenrod2")
(((class color) (min-colors 16) (background dark))
:background "blue3")
(((class color) (min-colors 16) (background light))
:background "lightgoldenrod2")
(((class color) (min-colors 8))
:background "blue" :foreground "white")
(((type tty) (class mono))
:inverse-video t)
(t :background "gray"))
"Basic face for highlighting the region."
:group 'basic-faces)
Internally, defface uses the symbol property
face-defface-spec to record the specified face attributes. The
attributes saved by the user with the customization buffer are
recorded in the symbol property saved-face; the attributes
customized by the user for the current session, but not saved, are
recorded in the symbol property customized-face. The
documentation string is recorded in the symbol property
face-documentation.
This option, if non-
nil, specifies the background type to use for interpreting face definitions. If it isdark, then Emacs treats all frames as if they had a dark background, regardless of their actual background colors. If it islight, then Emacs treats all frames as if they had a light background.
The effect of using a face is determined by a fixed set of face attributes. This table lists all the face attributes, their possible values, and their effects. You can specify more than one face for a given piece of text; Emacs merges the attributes of all the faces to determine how to display the text. See Displaying Faces.
In addition to the values given below, each face attribute can also
have the value unspecified. This special value means the face
doesn't specify that attribute. In face merging, when the first face
fails to specify a particular attribute, the next face gets a chance.
However, the default face must specify all attributes.
Some of these font attributes are meaningful only on certain kinds of displays. If your display cannot handle a certain attribute, the attribute is ignored.
:familyfont-family-list, described below,
returns a list of available family names. See Fontsets, for
information about fontsets.
:foundry:family attribute is located (a string). The wild-card
characters ‘*’ and ‘?’ are allowed.
:widthultra-condensed,
extra-condensed, condensed, semi-condensed,
normal, semi-expanded, expanded,
extra-expanded, or ultra-expanded.
:heightThe value can also be a floating point number or a function, which specifies the height relative to an underlying face (i.e., a face that has a lower priority in the list described in Displaying Faces). If the value is a floating point number, that specifies the amount by which to scale the height of the underlying face. If the value is a function, that function is called with one argument, the height of the underlying face, and returns the height of the new face. If the function is passed an integer argument, it must return an integer.
The height of the default face must be specified using an integer;
floating point and function values are not allowed.
:weightultra-bold, extra-bold, bold, semi-bold,
normal, semi-light, light, extra-light, or
ultra-light. On text-only terminals that support
variable-brightness text, any weight greater than normal is displayed
as extra bright, and any weight less than normal is displayed as
half-bright.
:slantitalic, oblique,
normal, reverse-italic, or reverse-oblique. On
text-only terminals that support variable-brightness text, slanted
text is displayed as half-bright.
:foreground:background:underlinet, underlining uses the foreground color of the
face. If the value is a string, underlining uses that color. The
value nil means do not underline.
:overline:underline.
:strike-through:underline.
:box:box attribute, and what they mean:
nilt(:line-width width :color color :style style)The value color specifies the color to draw with. The default is the foreground color of the face for simple boxes, and the background color of the face for 3D boxes.
The value style specifies whether to draw a 3D box. If it is
released-button, the box looks like a 3D button that is not being
pressed. If it is pressed-button, the box looks like a 3D button
that is being pressed. If it is nil or omitted, a plain 2D box
is used.
:inverse-videot (yes) or nil (no).
:stippleThe value can be a string; that should be the name of a file containing
external-format X bitmap data. The file is found in the directories
listed in the variable x-bitmap-file-path.
Alternatively, the value can specify the bitmap directly, with a list
of the form (width height data). Here,
width and height specify the size in pixels, and
data is a string containing the raw bits of the bitmap, row by
row. Each row occupies (width + 7) / 8 consecutive bytes
in the string (which should be a unibyte string for best results).
This means that each row always occupies at least one whole byte.
If the value is nil, that means use no stipple pattern.
Normally you do not need to set the stipple attribute, because it is
used automatically to handle certain shades of gray.
:fontWhen specifying this attribute using set-face-attribute
(see Attribute Functions), you may also supply a font spec, a font
entity, or a string. Emacs converts such values to an appropriate
font object, and stores that font object as the actual attribute
value. If you specify a string, the contents of the string should be
a font name (see Font Specification Options); if the font name is an XLFD containing wildcards,
Emacs chooses the first font matching those wildcards. Specifying
this attribute also changes the values of the :family,
:foundry, :width, :height, :weight, and
:slant attributes.
:inheritFor compatibility with Emacs 20, you can also specify values for two
“fake” face attributes: :bold and :italic. Their
values must be either t or nil; a value of
unspecified is not allowed. Setting :bold to t
is equivalent to setting the :weight attribute to bold,
and setting it to nil is equivalent to setting :weight
to normal. Setting :italic to t is equivalent to
setting the :slant attribute to italic, and setting it
to nil is equivalent to setting :slant to normal.
This function returns a list of available font family names. The optional argument frame specifies the frame on which the text is to be displayed; if it is
nil, the selected frame is used.
This variable specifies the minimum distance between the baseline and the underline, in pixels, when displaying underlined text.
This variable specifies a list of directories for searching for bitmap files, for the
:stippleattribute.
This returns
tif object is a valid bitmap specification, suitable for use with:stipple(see above). It returnsnilotherwise.
This section describes the functions for accessing and modifying the attributes of an existing face.
This function sets one or more attributes of face for frame. The attributes you specify this way override whatever the
deffacesays.The extra arguments arguments specify the attributes to set, and the values for them. They should consist of alternating attribute names (such as
:familyor:underline) and corresponding values. Thus,(set-face-attribute 'foo nil :width 'extended :weight 'bold :underline "red")sets the attributes
:width,:weightand:underlineto the corresponding values.If frame is
t, this function sets the default attributes for new frames. Default attribute values specified this way override thedeffacefor newly created frames.If frame is
nil, this function sets the attributes for all existing frames, and the default for new frames.
This returns the value of the attribute attribute of face on frame. If frame is
nil, that means the selected frame (see Input Focus).If frame is
t, this returns whatever new-frames default value you previously specified withset-face-attributefor the attribute attribute of face. If you have not specified one, it returnsnil.If inherit is
nil, only attributes directly defined by face are considered, so the return value may beunspecified, or a relative value. If inherit is non-nil, face's definition of attribute is merged with the faces specified by its:inheritattribute; however the return value may still beunspecifiedor relative. If inherit is a face or a list of faces, then the result is further merged with that face (or faces), until it becomes specified and absolute.To ensure that the return value is always specified and absolute, use a value of
defaultfor inherit; this will resolve any unspecified or relative values by merging with thedefaultface (which is always completely specified).For example,
(face-attribute 'bold :weight) ⇒ bold
This function returns non-
nilif value, when used as the value of the face attribute attribute, is relative. This means it would modify, rather than completely override, any value that comes from a subsequent face in the face list or that is inherited from another face.
unspecifiedis a relative value for all attributes. For:height, floating point and function values are also relative.For example:
(face-attribute-relative-p :height 2.0) ⇒ t
This function returns an alist of attributes of face. The elements of the result are name-value pairs of the form
(attr-name.attr-value). Optional argument frame specifies the frame whose definition of face to return; if omitted ornil, the returned value describes the default attributes of face for newly created frames.
If value1 is a relative value for the face attribute attribute, returns it merged with the underlying value value2; otherwise, if value1 is an absolute value for the face attribute attribute, returns value1 unchanged.
The following functions provide compatibility with Emacs 20 and
below. They work by calling set-face-attribute. Values of
t and nil for their frame argument are handled
just like set-face-attribute and face-attribute.
These functions set the
:foregroundattribute (or:backgroundattribute, respectively) of face to color.
This function sets the
:stippleattribute of face to pattern.
This function sets the
:fontattribute of face to font.
This function sets the
:weightattribute of face to normal if bold-p isnil, and to bold otherwise.
This function sets the
:slantattribute of face to normal if italic-p isnil, and to italic otherwise.
This function sets the
:underlineattribute of face to underline.
This function sets the
:inverse-videoattribute of face to inverse-video-p.
This function swaps the foreground and background colors of face face.
The following functions examine the attributes of a face. If you
don't specify frame, they refer to the selected frame; t
refers to the default data for new frames. They return the symbol
unspecified if the face doesn't define any value for that
attribute.
These functions return the foreground color (or background color, respectively) of face face, as a string.
If inherit is
nil, only a color directly defined by the face is returned. If inherit is non-nil, any faces specified by its:inheritattribute are considered as well, and if inherit is a face or a list of faces, then they are also considered, until a specified color is found. To ensure that the return value is always specified, use a value ofdefaultfor inherit.
This function returns the name of the background stipple pattern of face face, or
nilif it doesn't have one.If inherit is
nil, only a stipple directly defined by the face is returned. If inherit is non-nil, any faces specified by its:inheritattribute are considered as well, and if inherit is a face or a list of faces, then they are also considered, until a specified stipple is found. To ensure that the return value is always specified, use a value ofdefaultfor inherit.
This function returns a non-
nilvalue if the:weightattribute of face is bolder than normal (i.e., one ofsemi-bold,bold,extra-bold, orultra-bold). Otherwise, it returnsnil.
This function returns a non-
nilvalue if the:slantattribute of face isitalicoroblique, andnilotherwise.
This function returns the
:underlineattribute of face face.
This function returns the
:inverse-videoattribute of face face.
Here is how Emacs determines the face to use for displaying any given piece of text:
region face. See Standard Faces.
nil face
property, Emacs applies the face or face attributes specified by that
property. If the overlay has a mouse-face property and the
mouse is “near enough” to the overlay, Emacs applies the face or
face attributes specified by the mouse-face property instead.
See Overlay Properties.
When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See Overlays.
face or mouse-face property,
Emacs applies the specified faces and face attributes. See Special Properties. (This is how Font Lock mode faces are applied.
See Font Lock Mode.)
mode-line face. For the mode line of a
non-selected window, Emacs applies the mode-line-inactive face.
For a header line, Emacs applies the header-line face.
default face.
If these various sources together specify more than one face for a
particular character, Emacs merges the attributes of the various faces
specified. For each attribute, Emacs tries using the above order
(i.e., first the face of any special glyph; then the face for region
highlighting, if appropriate; then faces specified by overlays, then
faces specified by text properties, then the mode-line or
mode-line-inactive or header-line face, if appropriate,
and finally the default face).
The variable face-remapping-alist is used for buffer-local or
global changes in the appearance of a face. For instance, it can be
used to make the default face a variable-pitch face within a
particular buffer.
An alist whose elements have the form
(face remapping...). This causes Emacs to display text using the face face using remapping... instead of face's ordinary definition. remapping... may be any face specification suitable for afacetext property: either a face name, or a property list of attribute/value pairs. See Special Properties.If
face-remapping-alistis buffer-local, its local value takes effect only within that buffer.Two points bear emphasizing:
- The new definition remapping... is the complete specification of how to display face—it entirely replaces, rather than augmenting or modifying, the normal definition of that face.
- If remapping... recursively references the same face name face, either directly remapping entry, or via the
:inheritattribute of some other face in remapping..., then that reference uses the normal definition of face in the selected frame, instead of the “remapped” definition.For instance, if the
mode-lineface is remapped using this entry inface-remapping-alist:(mode-line italic mode-line)then the new definition of the
mode-lineface inherits from theitalicface, and the normal (non-remapped) definition ofmode-lineface.
A typical use of the face-remapping-alist is to change a
buffer's default face; for example, the following changes a
buffer's default face to use the variable-pitch face,
with the height doubled:
(set (make-local-variable 'face-remapping-alist)
'((default variable-pitch :height 2.0)))
The following functions implement a higher-level interface to
face-remapping-alist, making it easier to use
“cooperatively”. They are mainly intended for buffer-local use, and
so all make face-remapping-alist variable buffer-local as a
side-effect. They use entries in face-remapping-alist which
have the general form:
(face relative_specs_1 relative_specs_2 ... base_specs)
Everything except face is a “face spec”: a list of face names or face attribute-value pairs. All face specs are merged together, with earlier values taking precedence.
The relative_specs_n values are “relative specs”, and are
added by face-remap-add-relative (and removed by
face-remap-remove-relative. These are intended for face
modifications (such as increasing the size). Typical users of these
relative specs would be minor modes.
base_specs is the lowest-priority value, and by default is just the face name, which causes the global definition of that face to be used.
A non-default value of base_specs may also be set using
face-remap-set-base. Because this overwrites the
default base-spec value (which inherits the global face definition),
it is up to the caller of face-remap-set-base to add such
inheritance if it is desired. A typical use of
face-remap-set-base would be a major mode adding a face
remappings, e.g., of the default face.
This functions adds a face remapping entry of face to specs in the current buffer.
It returns a “cookie” which can be used to later delete the remapping with
face-remap-remove-relative.specs can be any value suitable for the
facetext property, including a face name, a list of face names, or a face-attribute property list. The attributes given by specs will be merged with any other currently active face remappings of face, and with the global definition of face (by default; this may be changed usingface-remap-set-base), with the most recently added relative remapping taking precedence.
This function removes a face remapping previously added by
face-remap-add-relative. cookie should be a return value from that function.
This function sets the “base remapping” of face in the current buffer to specs. If specs is empty, the default base remapping is restored, which inherits from the global definition of face; note that this is different from specs containing a single value
nil, which has the opposite result (the global definition of face is ignored).
This function sets the “base remapping” of face to its default value, which inherits from face's global definition.
Here are additional functions for creating and working with faces.
This function defines a new face named name, initially with all attributes
nil. It does nothing if there is already a face named name.
This function defines a face named new-name as a copy of the existing face named old-face. It creates the face new-name if that doesn't already exist.
If the optional argument frame is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from old-face in each frame to new-face in the same frame.
If the optional argument new-frame is given, then
copy-facecopies the attributes of old-face in frame to new-name in new-frame.
This function returns the face number of face face. This is a number that uniquely identifies a face at low levels within Emacs. It is seldom necessary to refer to a face by its face number.
This function returns the documentation string of face face, or
nilif none was specified for it.
This returns
tif the faces face1 and face2 have the same attributes for display.
This returns non-
nilif the face face displays differently from the default face.
A face alias provides an equivalent name for a face. You can
define a face alias by giving the alias symbol the face-alias
property, with a value of the target face name. The following example
makes modeline an alias for the mode-line face.
(put 'modeline 'face-alias 'mode-line)
This function defines a face alias and marks it as obsolete, indicating that it may be removed in future. The optional string when indicates when the face was made obsolete (for example, a release number).
This hook is used for automatically assigning faces to text in the buffer. It is part of the implementation of Jit-Lock mode, used by Font-Lock.
This variable holds a list of functions that are called by Emacs redisplay as needed, just before doing redisplay. They are called even when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this variable usually holds just one function,
jit-lock-function.The functions are called in the order listed, with one argument, a buffer position pos. Collectively they should attempt to assign faces to the text in the current buffer starting at pos.
The functions should record the faces they assign by setting the
faceproperty. They should also add a non-nilfontifiedproperty to all the text they have assigned faces to. That property tells redisplay that faces have been assigned to that text already.It is probably a good idea for the functions to do nothing if the character after pos already has a non-
nilfontifiedproperty, but this is not required. If one function overrides the assignments made by a previous one, the properties after the last function finishes are the ones that really matter.For efficiency, we recommend writing these functions so that they usually assign faces to around 400 to 600 characters at each call.
Before Emacs can draw a character on a particular display, it must
select a font for that character17. Normally, Emacs automatically chooses a font based on the
faces assigned to that character—specifically, the face attributes
:family, :weight, :slant, and :width
(see Face Attributes). The choice of font also depends on the
character to be displayed; some fonts can only display a limited set
of characters. If no available font exactly fits the requirements,
Emacs looks for the closest matching font. The variables in
this section control how Emacs makes this selection.
If a given family is specified but does not exist, this variable specifies alternative font families to try. Each element should have this form:
(family alternate-families...)If family is specified but not available, Emacs will try the other families given in alternate-families, one by one, until it finds a family that does exist.
If there is no font that exactly matches all desired face attributes (
:width,:height,:weight, and:slant), this variable specifies the order in which these attributes should be considered when selecting the closest matching font. The value should be a list containing those four attribute symbols, in order of decreasing importance. The default is(:width :height :weight :slant).Font selection first finds the best available matches for the first attribute in the list; then, among the fonts which are best in that way, it searches for the best matches in the second attribute, and so on.
The attributes
:weightand:widthhave symbolic values in a range centered aroundnormal. Matches that are more extreme (farther fromnormal) are somewhat preferred to matches that are less extreme (closer tonormal); this is designed to ensure that non-normal faces contrast with normal ones, whenever possible.One example of a case where this variable makes a difference is when the default font has no italic equivalent. With the default ordering, the
italicface will use a non-italic font that is similar to the default one. But if you put:slantbefore:height, theitalicface will use an italic font, even if its height is not quite right.
This variable lets you specify alternative font registries to try, if a given registry is specified and doesn't exist. Each element should have this form:
(registry alternate-registries...)If registry is specified but not available, Emacs will try the other registries given in alternate-registries, one by one, until it finds a registry that does exist.
Emacs can make use of scalable fonts, but by default it does not use them.
This variable controls which scalable fonts to use. A value of
nil, the default, means do not use scalable fonts.tmeans to use any scalable font that seems appropriate for the text.Otherwise, the value must be a list of regular expressions. Then a scalable font is enabled for use if its name matches any regular expression in the list. For example,
(setq scalable-fonts-allowed '("muleindian-2$"))allows the use of scalable fonts with registry
muleindian-2.
This variable specifies scaling for certain faces. Its value should be a list of elements of the form
(fontname-regexp . scale-factor)If fontname-regexp matches the font name that is about to be used, this says to choose a larger similar font according to the factor scale-factor. You would use this feature to normalize the font size if certain fonts are bigger or smaller than their nominal heights and widths would suggest.
This function returns a list of available font names that match name. name should be a string containing a font name in either the Fontconfig, GTK, or XLFD format (see Font Specification Options). Within an XLFD string, wildcard characters may be used: the ‘*’ character matches any substring, and the ‘?’ character matches any single character. Case is ignored when matching font names.
If the optional arguments reference-face and frame are specified, the returned list includes only fonts that are the same size as reference-face (a face name) currently is on the frame frame.
The optional argument maximum sets a limit on how many fonts to return. If it is non-
nil, then the return value is truncated after the first maximum matching fonts. Specifying a small value for maximum can make this function much faster, in cases where many fonts match the pattern.The optional argument width specifies a desired font width. If it is non-
nil, the function only returns those fonts whose characters are (on average) width times as wide as reference-face.
This function returns a list describing the available fonts for family family on frame. If family is omitted or
nil, this list applies to all families, and therefore, it contains all available fonts. Otherwise, family must be a string; it may contain the wildcards ‘?’ and ‘*’.The list describes the display that frame is on; if frame is omitted or
nil, it applies to the selected frame's display (see Input Focus).Each element in the list is a vector of the following form:
[family width point-size weight slant fixed-p full registry-and-encoding]The first five elements correspond to face attributes; if you specify these attributes for a face, it will use this font.
The last three elements give additional information about the font. fixed-p is non-
nilif the font is fixed-pitch. full is the full name of the font, and registry-and-encoding is a string giving the registry and encoding of the font.
This variable specifies maximum number of fonts to consider in font matching. The function
x-family-fontswill not return more than that many fonts, and font selection will consider only that many fonts when searching a matching font for face attributes. The default is currently 100.
A fontset is a list of fonts, each assigned to a range of character codes. An individual font cannot display the whole range of characters that Emacs supports, but a fontset can. Fontsets have names, just as fonts do, and you can use a fontset name in place of a font name when you specify the “font” for a frame or a face. Here is information about defining a fontset under Lisp program control.
This function defines a new fontset according to the specification string fontset-spec. The string should have this format:
fontpattern, [charset:font]...Whitespace characters before and after the commas are ignored.
The first part of the string, fontpattern, should have the form of a standard X font name, except that the last two fields should be ‘fontset-alias’.
The new fontset has two names, one long and one short. The long name is fontpattern in its entirety. The short name is ‘fontset-alias’. You can refer to the fontset by either name. If a fontset with the same name already exists, an error is signaled, unless noerror is non-
nil, in which case this function does nothing.If optional argument style-variant-p is non-
nil, that says to create bold, italic and bold-italic variants of the fontset as well. These variant fontsets do not have a short name, only a long one, which is made by altering fontpattern to indicate the bold or italic status.The specification string also says which fonts to use in the fontset. See below for the details.
The construct ‘charset:font’ specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in the specification string.
For the remaining character sets, those that you don't specify explicitly, Emacs chooses a font based on fontpattern: it replaces ‘fontset-alias’ with a value that names one character set. For the ASCII character set, ‘fontset-alias’ is replaced with ‘ISO8859-1’.
In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which Emacs does.
Thus if fontpattern is this,
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
the font specification for ASCII characters would be this:
-*-fixed-medium-r-normal-*-24-*-ISO8859-1
and the font specification for Chinese GB2312 characters would be this:
-*-fixed-medium-r-normal-*-24-*-gb2312*-*
You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have ‘song ti’ or ‘fangsong ti’ in the family field. In such a case, ‘Fontset-n’ can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
Then, the font specifications for all but Chinese GB2312 characters have ‘fixed’ in the family field, and the font specification for Chinese GB2312 characters has a wild card ‘*’ in the family field.
This function modifies the existing fontset name to use the font matching with font-spec for the character character.
If name is
nil, this function modifies the fontset of the selected frame or that of frame if frame is notnil.If name is
t, this function modifies the default fontset, whose short name is ‘fontset-default’.character may be a cons;
(from.to), where from and to are character codepoints. In that case, use font-spec for all characters in the range from and to (inclusive).character may be a charset. In that case, use font-spec for all character in the charsets.
character may be a script name. In that case, use font-spec for all character in the charsets.
font-spec may be a cons;
(family.registry), where family is a family name of a font (possibly including a foundry name at the head), registry is a registry name of a font (possibly including an encoding name at the tail).font-spec may be a font name string.
The optional argument add, if non-
nil, specifies how to add font-spec to the font specifications previously set. If it isprepend, font-spec is prepended. If it isappend, font-spec is appended. By default, font-spec overrides the previous settings.For instance, this changes the default fontset to use a font of which family name is ‘Kochi Gothic’ for all characters belonging to the charset
japanese-jisx0208.(set-fontset-font t 'japanese-jisx0208 (font-spec :family "Kochi Gothic"))
This function returns
tif Emacs ought to be able to display char. More precisely, if the selected frame's fontset has a font to display the character set that char belongs to.Fontsets can specify a font on a per-character basis; when the fontset does that, this function's value may not be accurate.
Normally, it is not necessary to manipulate fonts directly. In case you need to do so, this section explains how.
In Emacs Lisp, fonts are represented using three different Lisp object types: font objects, font specs, and font entities.
Return
tif object is a font object, font spec, or font entity. Otherwise, returnnil.The optional argument type, if non-
nil, determines the exact type of Lisp object to check for. In that case, type should be one offont-object,font-spec, orfont-entity.
A font object is a Lisp object that represents a font that Emacs has opened. Font objects cannot be modified in Lisp, but they can be inspected.
Return the font object that is being used to display the character at position position in the window window. If window is
nil, it defaults to the selected window. If string isnil, position specifies a position in the current buffer; otherwise, string should be a string, and position specifies a position in that string.
A font spec is a Lisp object that contains a set of specifications that can be used to find a font. More than one font may match the specifications in a font spec.
Return a new font spec using the specifications in arguments, which should come in
property-valuepairs. The possible specifications are as follows:
:name- The font name (a string), in either XLFD, Fontconfig, or GTK format. See Font Specification Options.
:family:foundry:weight:slant:width- These have the same meanings as the face attributes of the same name. See Face Attributes.
:size- The font size—either a non-negative integer that specifies the pixel size, or a floating point number that specifies the point size.
:adstyle- Additional typographic style information for the font, such as ‘sans’. The value should be a string or a symbol.
:registry- The charset registry and encoding of the font, such as ‘iso8859-1’. The value should be a string or a symbol.
:script- The script that the font must support (a symbol).
:otf- The font must be an OpenType font that supports these OpenType features, provided Emacs is compiled with support for ‘libotf’ (a library for performing complex text layout in certain scripts). The value must be a list of the form
(script-tag langsys-tag gsub gpos)where script-tag is the OpenType script tag symbol; langsys-tag is the OpenType language system tag symbol, or
nilto use the default language system;gsubis a list of OpenType GSUB feature tag symbols, ornilif none is required; andgposis a list of OpenType GPOS feature tag symbols, ornilif none is required. Ifgsuborgposis a list, anilelement in that list means that the font must not match any of the remaining tag symbols. Thegposelement may be omitted.
Set the font property property in the font-spec font-spec to value.
A font entity is a reference to a font that need not be open. Its properties are intermediate between a font object and a font spec: like a font object, and unlike a font spec, it refers to a single, specific font. Unlike a font object, creating a font entity does not load the contents of that font into computer memory.
This function returns a font entity that best matches the font spec font-spec on frame frame. If frame is
nil, it defaults to the selected frame.
This function returns a list of all font entities that match the font spec font-spec.
The optional argument frame, if non-
nil, specifies the frame on which the fonts are to be displayed. The optional argument num, if non-nil, should be an integer that specifies the maximum length of the returned list. The optional argument prefer, if non-nil, should be another font spec, which is used to control the order of the returned list; the returned font entities are sorted in order of decreasing “closeness” to that font spec.
If you call set-face-attribute and pass a font spec, font
entity, or font name string as the value of the :font
attribute, Emacs opens the best “matching” font that is available
for display. It then stores the corresponding font object as the
actual value of the :font attribute for that face.
The following functions can be used to obtain information about a font. For these functions, the font argument can be a font object, a font entity, or a font spec.
This function returns the value of the font property property for font.
If font is a font spec and the font spec does not specify property, the return value is
nil. If font is a font object or font entity, the value for the :script property may be a list of scripts supported by the font.
This function returns a list of face attributes corresponding to font. The optional argument frame specifies the frame on which the font is to be displayed. If it is
nil, the selected frame is used. The return value has the form(:family family :height height :weight weight :slant slant :width width)where the values of family, height, weight, slant, and width are face attribute values. Some of these key-attribute pairs may be omitted from the list if they are not specified by font.
This function returns the XLFD (X Logical Font Descriptor), a string, matching font. See Font Specification Options, for information about XLFDs. If the name is too long for an XLFD (which can contain at most 255 characters), the function returns
nil.If the optional argument fold-wildcards is non-
nil, consecutive wildcards in the XLFD are folded into one.
The fringes of a window are thin vertical strips down the sides that are used for displaying bitmaps that indicate truncation, continuation, horizontal scrolling, and the overlay arrow.
The following buffer-local variables control the position and width of the window fringes.
The fringes normally appear between the display margins and the window text. If the value is non-
nil, they appear outside the display margins. See Display Margins.
This variable, if non-
nil, specifies the width of the left fringe in pixels. A value ofnilmeans to use the left fringe width from the window's frame.
This variable, if non-
nil, specifies the width of the right fringe in pixels. A value ofnilmeans to use the right fringe width from the window's frame.
The values of these variables take effect when you display the
buffer in a window. If you change them while the buffer is visible,
you can call set-window-buffer to display it once again in the
same window, to make the changes take effect.
This function sets the fringe widths of window window. If window is
nil, the selected window is used.The argument left specifies the width in pixels of the left fringe, and likewise right for the right fringe. A value of
nilfor either one stands for the default width. If outside-margins is non-nil, that specifies that fringes should appear outside of the display margins.
This function returns information about the fringes of a window window. If window is omitted or
nil, the selected window is used. The value has the form(left-width right-width outside-margins).
The fringe indicators are tiny icons Emacs displays in the window fringe (on a graphic display) to indicate truncated or continued lines, buffer boundaries, overlay arrow, etc.
When this is non-
nil, Emacs displays a special glyph in the fringe of each empty line at the end of the buffer, on graphical displays. See Fringes. This variable is automatically buffer-local in every buffer.
This buffer-local variable controls how the buffer boundaries and window scrolling are indicated in the window fringes.
Emacs can indicate the buffer boundaries—that is, the first and last line in the buffer—with angle icons when they appear on the screen. In addition, Emacs can display an up-arrow in the fringe to show that there is text above the screen, and a down-arrow to show there is text below the screen.
There are three kinds of basic values:
nil- Don't display any of these fringe icons.
left- Display the angle icons and arrows in the left fringe.
right- Display the angle icons and arrows in the right fringe.
- any non-alist
- Display the angle icons in the left fringe and don't display the arrows.
Otherwise the value should be an alist that specifies which fringe indicators to display and where. Each element of the alist should have the form
(indicator.position). Here, indicator is one oftop,bottom,up,down, andt(which covers all the icons not yet specified), while position is one ofleft,rightandnil.For example,
((top . left) (t . right))places the top angle bitmap in left fringe, and the bottom angle bitmap as well as both arrow bitmaps in right fringe. To show the angle bitmaps in the left fringe, and no arrow bitmaps, use((top . left) (bottom . left)).
This buffer-local variable specifies the mapping from logical fringe indicators to the actual bitmaps displayed in the window fringes.
These symbols identify the logical fringe indicators:
- Truncation and continuation line indicators:
truncation,continuation.- Buffer position indicators:
up,down,top,bottom,top-bottom.- Empty line indicator:
empty-line.- Overlay arrow indicator:
overlay-arrow.- Unknown bitmap indicator:
unknown.The value is an alist where each element
(indicator.bitmaps)specifies the fringe bitmaps used to display a specific logical fringe indicator.Here, indicator specifies the logical indicator type, and bitmaps is list of symbols
(left right[left1 right1])which specifies the actual bitmap shown in the left or right fringe for the logical indicator.The left and right symbols specify the bitmaps shown in the left and/or right fringe for the specific indicator. The left1 or right1 bitmaps are used only for the `bottom' and `top-bottom indicators when the last (only) line in has no final newline. Alternatively, bitmaps may be a single symbol which is used in both left and right fringes.
When
fringe-indicator-alisthas a buffer-local value, and there is no bitmap defined for a logical indicator, or the bitmap ist, the corresponding value from the default value offringe-indicator-alistis used.To completely hide a specific indicator, set the bitmap to
nil.
Standard fringe bitmaps for indicators:
left-arrow right-arrow up-arrow down-arrow
left-curly-arrow right-curly-arrow
left-triangle right-triangle
top-left-angle top-right-angle
bottom-left-angle bottom-right-angle
left-bracket right-bracket
filled-rectangle hollow-rectangle
filled-square hollow-square
vertical-bar horizontal-bar
empty-line question-mark
When a line is exactly as wide as the window, Emacs displays the cursor in the right fringe instead of using two lines. Different bitmaps are used to represent the cursor in the fringe depending on the current buffer's cursor type.
box , hollow, bar,
hbar, hollow-small.
The hollow-small type is used instead of hollow when the
normal hollow-rectangle bitmap is too tall to fit on a specific
display line.
If this is non-
nil, lines exactly as wide as the window (not counting the final newline character) are not continued. Instead, when point is at the end of the line, the cursor appears in the right fringe.
This variable specifies the mapping from logical cursor type to the actual fringe bitmaps displayed in the right fringe. The value is an alist where each element
(cursor.bitmap)specifies the fringe bitmaps used to display a specific logical cursor type in the fringe. Here, cursor specifies the logical cursor type and bitmap is a symbol specifying the fringe bitmap to be displayed for that logical cursor type.When
fringe-cursor-alisthas a buffer-local value, and there is no bitmap defined for a cursor type, the corresponding value from the default value offringes-indicator-alistis used.
Standard bitmaps for displaying the cursor in right fringe:
filled-rectangle hollow-rectangle filled-square hollow-square
vertical-bar horizontal-bar
The fringe bitmaps are the actual bitmaps which represent the logical fringe indicators for truncated or continued lines, buffer boundaries, overlay arrow, etc. Fringe bitmap symbols have their own name space. The fringe bitmaps are shared by all frames and windows. You can redefine the built-in fringe bitmaps, and you can define new fringe bitmaps.
The way to display a bitmap in the left or right fringes for a given
line in a window is by specifying the display property for one
of the characters that appears in it. Use a display specification of
the form (left-fringe bitmap [face]) or
(right-fringe bitmap [face]) (see Display Property). Here, bitmap is a symbol identifying the bitmap you
want, and face (which is optional) is the name of the face whose
colors should be used for displaying the bitmap, instead of the
default fringe face. face is automatically merged with
the fringe face, so normally face need only specify the
foreground color for the bitmap.
This function returns the fringe bitmaps of the display line containing position pos in window window. The return value has the form
(left right ov), where left is the symbol for the fringe bitmap in the left fringe (ornilif no bitmap), right is similar for the right fringe, and ov is non-nilif there is an overlay arrow in the left fringe.The value is
nilif pos is not visible in window. If window isnil, that stands for the selected window. If pos isnil, that stands for the value of point in window.
This function defines the symbol bitmap as a new fringe bitmap, or replaces an existing bitmap with that name.
The argument bits specifies the image to use. It should be either a string or a vector of integers, where each element (an integer) corresponds to one row of the bitmap. Each bit of an integer corresponds to one pixel of the bitmap, where the low bit corresponds to the rightmost pixel of the bitmap.
The height is normally the length of bits. However, you can specify a different height with non-
nilheight. The width is normally 8, but you can specify a different width with non-nilwidth. The width must be an integer between 1 and 16.The argument align specifies the positioning of the bitmap relative to the range of rows where it is used; the default is to center the bitmap. The allowed values are
top,center, orbottom.The align argument may also be a list
(align periodic)where align is interpreted as described above. If periodic is non-nil, it specifies that the rows inbitsshould be repeated enough times to reach the specified height.
This function destroy the fringe bitmap identified by bitmap. If bitmap identifies a standard fringe bitmap, it actually restores the standard definition of that bitmap, instead of eliminating it entirely.
This sets the face for the fringe bitmap bitmap to face. If face is
nil, it selects thefringeface. The bitmap's face controls the color to draw it in.face is merged with the
fringeface, so normally face should specify only the foreground color.
The overlay arrow is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed. This feature has nothing to do with overlays (see Overlays).
This variable holds the string to display to call attention to a particular line, or
nilif the arrow feature is not in use. On a graphical display the contents of the string are ignored; instead a glyph is displayed in the fringe area to the left of the display area.
This variable holds a marker that indicates where to display the overlay arrow. It should point at the beginning of a line. On a non-graphical display the arrow text appears at the beginning of that line, overlaying any text that would otherwise appear. Since the arrow is usually short, and the line usually begins with indentation, normally nothing significant is overwritten.
The overlay-arrow string is displayed in any given buffer if the value of
overlay-arrow-positionin that buffer points into that buffer. Thus, it is possible to display multiple overlay arrow strings by creating buffer-local bindings ofoverlay-arrow-position. However, it is usually cleaner to useoverlay-arrow-variable-listto achieve this result.
You can do a similar job by creating an overlay with a
before-string property. See Overlay Properties.
You can define multiple overlay arrows via the variable
overlay-arrow-variable-list.
This variable's value is a list of variables, each of which specifies the position of an overlay arrow. The variable
overlay-arrow-positionhas its normal meaning because it is on this list.
Each variable on this list can have properties
overlay-arrow-string and overlay-arrow-bitmap that
specify an overlay arrow string (for text-only terminals) or fringe
bitmap (for graphical terminals) to display at the corresponding
overlay arrow position. If either property is not set, the default
overlay-arrow-string or overlay-arrow fringe indicator
is used.
Normally the frame parameter vertical-scroll-bars controls
whether the windows in the frame have vertical scroll bars, and
whether they are on the left or right. The frame parameter
scroll-bar-width specifies how wide they are (nil
meaning the default). See Layout Parameters.
This function reports the scroll bar type settings for frame frame. The value is a cons cell
(vertical-type.horizontal-type), where vertical-type is eitherleft,right, ornil(which means no scroll bar.) horizontal-type is meant to specify the horizontal scroll bar type, but since they are not implemented, it is alwaysnil.
You can enable or disable scroll bars for a particular buffer,
by setting the variable vertical-scroll-bar. This variable
automatically becomes buffer-local when set. The possible values are
left, right, t, which means to use the
frame's default, and nil for no scroll bar.
You can also control this for individual windows. Call the function
set-window-scroll-bars to specify what to do for a specific window:
This function sets the width and type of scroll bars for window window.
width specifies the scroll bar width in pixels (
nilmeans use the width specified for the frame). vertical-type specifies whether to have a vertical scroll bar and, if so, where. The possible values areleft,rightandnil, just like the values of thevertical-scroll-barsframe parameter.The argument horizontal-type is meant to specify whether and where to have horizontal scroll bars, but since they are not implemented, it has no effect. If window is
nil, the selected window is used.
Report the width and type of scroll bars specified for window. If window is omitted or
nil, the selected window is used. The value is a list of the form(width cols vertical-type horizontal-type). The value width is the value that was specified for the width (which may benil); cols is the number of columns that the scroll bar actually occupies.horizontal-type is not actually meaningful.
If you don't specify these values for a window with
set-window-scroll-bars, the buffer-local variables
scroll-bar-mode and scroll-bar-width in the buffer being
displayed control the window's vertical scroll bars. The function
set-window-buffer examines these variables. If you change them
in a buffer that is already visible in a window, you can make the
window take note of the new values by calling set-window-buffer
specifying the same buffer that is already displayed.
This variable, always local in all buffers, controls whether and where to put scroll bars in windows displaying the buffer. The possible values are
nilfor no scroll bar,leftto put a scroll bar on the left, andrightto put a scroll bar on the right.
This function reports the scroll bar type for window window. If window is omitted or
nil, the selected window is used. The value is a cons cell(vertical-type.horizontal-type). Unlikewindow-scroll-bars, this reports the scroll bar type actually used, once frame defaults andscroll-bar-modeare taken into account.
This variable, always local in all buffers, specifies the width of the buffer's scroll bars, measured in pixels. A value of
nilmeans to use the value specified by the frame.
display Property
The display text property (or overlay property) is used to
insert images into text, and also control other aspects of how text
displays. The value of the display property should be a
display specification, or a list or vector containing several display
specifications. Display specifications in the same display
property value generally apply in parallel to the text they cover.
If several sources (overlays and/or a text property) specify values
for the display property, only one of the values takes effect,
following the rules of get-char-property. See Examining Properties.
The rest of this section describes several kinds of display specifications and what they mean.
Some kinds of display specifications specify something to
display instead of the text that has the property. These are called
replacing display specifications. Emacs does not allow the user
to interactively move point into the middle of buffer text that is
replaced in this way.
If a list of display specifications includes more than one replacing display specification, the first overrides the rest. Replacing display specifications make most other display specifications irrelevant, since those don't apply to the replacement.
For replacing display specifications, “the text that has the
property” means all the consecutive characters that have the same
Lisp object as their display property; these characters are
replaced as a single unit. By contrast, characters that have similar
but distinct Lisp objects as their display properties are
handled separately. Here's a function that illustrates this point:
(defun foo ()
(goto-char (point-min))
(dotimes (i 5)
(let ((string (concat "A")))
(put-text-property (point) (1+ (point)) 'display string)
(forward-char 1)
(put-text-property (point) (1+ (point)) 'display string)
(forward-char 1))))
It gives each of the first ten characters in the buffer string
"A" as the display property, but they don't all get the
same string. The first two characters get the same string, so they
together are replaced with one ‘A’. The next two characters get
a second string, so they together are replaced with one ‘A’.
Likewise for each following pair of characters. Thus, the ten
characters appear as five A's. This function would have the same
results:
(defun foo ()
(goto-char (point-min))
(dotimes (i 5)
(let ((string (concat "A")))
(put-text-property (point) (+ 2 (point)) 'display string)
(put-text-property (point) (1+ (point)) 'display string)
(forward-char 2))))
This illustrates that what matters is the property value for
each character. If two consecutive characters have the same
object as the display property value, it's irrelevant
whether they got this property from a single call to
put-text-property or from two different calls.
To display a space of specified width and/or height, use a display
specification of the form (space . props), where
props is a property list (a list of alternating properties and
values). You can put this property on one or more consecutive
characters; a space of the specified height and width is displayed in
place of all of those characters. These are the properties you
can use in props to specify the weight of the space:
:width width:relative-width factordisplay property. The space width is the width of that
character, multiplied by factor.
:align-to hposYou should use one and only one of the above properties. You can also specify the height of the space, with these properties:
:height height:relative-height factor:ascent ascentDon't use both :height and :relative-height together.
The :width and :align-to properties are supported on
non-graphic terminals, but the other space properties in this section
are not.
The value of the :width, :align-to, :height,
and :ascent properties can be a special kind of expression that
is evaluated during redisplay. The result of the evaluation is used
as an absolute number of pixels.
The following expressions are supported:
expr ::= num | (num) | unit | elem | pos | image | form
num ::= integer | float | symbol
unit ::= in | mm | cm | width | height
elem ::= left-fringe | right-fringe | left-margin | right-margin
| scroll-bar | text
pos ::= left | center | right
form ::= (num . expr) | (op expr ...)
op ::= + | -
The form num specifies a fraction of the default frame font
height or width. The form (num) specifies an absolute
number of pixels. If num is a symbol, symbol, its
buffer-local variable binding is used.
The in, mm, and cm units specify the number of
pixels per inch, millimeter, and centimeter, respectively. The
width and height units correspond to the default width
and height of the current face. An image specification image
corresponds to the width or height of the image.
The left-fringe, right-fringe, left-margin,
right-margin, scroll-bar, and text elements
specify to the width of the corresponding area of the window.
The left, center, and right positions can be
used with :align-to to specify a position relative to the left
edge, center, or right edge of the text area.
Any of the above window elements (except text) can also be
used with :align-to to specify that the position is relative to
the left edge of the given area. Once the base offset for a relative
position has been set (by the first occurrence of one of these
symbols), further occurrences of these symbols are interpreted as the
width of the specified area. For example, to align to the center of
the left-margin, use
:align-to (+ left-margin (0.5 . left-margin))
If no specific base offset is set for alignment, it is always relative to the left edge of the text area. For example, ‘:align-to 0’ in a header-line aligns with the first text column in the text area.
A value of the form (num . expr) stands for the
product of the values of num and expr. For example,
(2 . in) specifies a width of 2 inches, while (0.5 .
image) specifies half the width (or height) of the specified
image.
The form (+ expr ...) adds up the value of the
expressions. The form (- expr ...) negates or subtracts
the value of the expressions.
Here are the other sorts of display specifications that you can use
in the display text property.
Recursive display specifications are not supported—string's
display properties, if any, are not used.
(image . image-props)(slice x y width height)image specifies a slice
(a partial area) of the image to display. The elements y and
x specify the top left corner of the slice, within the image;
width and height specify the width and height of the
slice. Integer values are numbers of pixels. A floating point number
in the range 0.0–1.0 stands for that fraction of the width or height
of the entire image.
((margin nil) string)(left-fringe bitmap [face])(right-fringe bitmap [face])(space-width factor)(height height)(+ n)(- n)height bound to the current specified font height.
(raise factor)factor must be a number, which is interpreted as a multiple of the height of the affected text. If it is positive, that means to display the characters raised. If it is negative, that means to display them lower down.
If the text also has a height display specification, that does
not affect the amount of raising or lowering, which is based on the
faces used for the text.
You can make any display specification conditional. To do that,
package it in another list of the form
(when condition . spec).
Then the specification spec applies only when
condition evaluates to a non-nil value. During the
evaluation, object is bound to the string or buffer having the
conditional display property. position and
buffer-position are bound to the position within object
and the buffer position where the display property was found,
respectively. Both positions can be different when object is a
string.
A buffer can have blank areas called display margins on the
left and on the right. Ordinary text never appears in these areas,
but you can put things into the display margins using the
display property. There is currently no way to make text or
images in the margin mouse-sensitive.
The way to display something in the margins is to specify it in a
margin display specification in the display property of some
text. This is a replacing display specification, meaning that the
text you put it on does not get displayed; the margin display appears,
but that text does not.
A margin display specification looks like ((margin
right-margin) spec) or ((margin left-margin) spec).
Here, spec is another display specification that says what to
display in the margin. Typically it is a string of text to display,
or an image descriptor.
To display something in the margin in association with
certain buffer text, without altering or preventing the display of
that text, put a before-string property on the text and put the
margin display specification on the contents of the before-string.
Before the display margins can display anything, you must give them a nonzero width. The usual way to do that is to set these variables:
This variable specifies the width of the left margin. It is buffer-local in all buffers.
This variable specifies the width of the right margin. It is buffer-local in all buffers.
Setting these variables does not immediately affect the window. These
variables are checked when a new buffer is displayed in the window.
Thus, you can make changes take effect by calling
set-window-buffer.
You can also set the margin widths immediately.
This function specifies the margin widths for window window. The argument left controls the left margin and right controls the right margin (default
0).
This function returns the left and right margins of window as a cons cell of the form
(left.right). If window isnil, the selected window is used.
To display an image in an Emacs buffer, you must first create an image
descriptor, then use it as a display specifier in the display
property of text that is displayed (see Display Property).
Emacs is usually able to display images when it is run on a
graphical terminal. Images cannot be displayed in a text terminal, on
certain graphical terminals that lack the support for this, or if
Emacs is compiled without image support. You can use the function
display-images-p to determine if images can in principle be
displayed (see Display Feature Testing).
Emacs can display a number of different image formats; some of them
are supported only if particular support libraries are installed on
your machine. In some environments, Emacs can load image
libraries on demand; if so, the variable image-library-alist
can be used to modify the set of known names for these dynamic
libraries (though it is not possible to add new image formats).
The supported image formats include XBM, XPM (this requires the
libraries libXpm version 3.4k and libz), GIF (requiring
libungif 4.1.0), PostScript, PBM, JPEG (requiring the
libjpeg library version v6a), TIFF (requiring libtiff
v3.4), PNG (requiring libpng 1.0.2), and SVG (requiring
librsvg 2.0.0).
You specify one of these formats with an image type symbol. The image
type symbols are xbm, xpm, gif, postscript,
pbm, jpeg, tiff, png, and svg.
This variable contains a list of those image type symbols that are potentially supported in the current configuration. Potentially here means that Emacs knows about the image types, not necessarily that they can be loaded (they could depend on unavailable dynamic libraries, for example).
To know which image types are really available, use
image-type-available-p.
This in an alist of image types vs external libraries needed to display them.
Each element is a list
(image-type library...), where the car is a supported image format fromimage-types, and the rest are strings giving alternate filenames for the corresponding external libraries to load.Emacs tries to load the libraries in the order they appear on the list; if none is loaded, the running session of Emacs won't support the image type.
pbmandxbmdon't need to be listed; they're always supported.This variable is ignored if the image libraries are statically linked into Emacs.
This function returns non-
nilif image type type is available, i.e., if images of this type can be loaded and displayed in Emacs. type should be one of the types contained inimage-types.For image types whose support libraries are statically linked, this function always returns
t; for other image types, it returnstif the dynamic library could be loaded,nilotherwise.
An image description is a list of the form (image . props),
where props is a property list containing alternating keyword
symbols (symbols whose names start with a colon) and their values.
You can use any Lisp object as a property, but the only properties
that have any special meaning are certain symbols, all of them keywords.
Every image descriptor must contain the property :type
type to specify the format of the image. The value of type
should be an image type symbol; for example, xpm for an image in
XPM format.
Here is a list of other properties that are meaningful for all image types:
:file file:file property says to load the image from file
file. If file is not an absolute file name, it is expanded
in data-directory.
:data data:data property says the actual contents of the image.
Each image must use either :data or :file, but not both.
For most image types, the value of the :data property should be a
string containing the image data; we recommend using a unibyte string.
Before using :data, look for further information in the section
below describing the specific image format. For some image types,
:data may not be supported; for some, it allows other data types;
for some, :data alone is not enough, so you need to use other
image properties along with :data.
:margin margin:margin property specifies how many pixels to add as an
extra margin around the image. The value, margin, must be a
non-negative number, or a pair (x . y) of such
numbers. If it is a pair, x specifies how many pixels to add
horizontally, and y specifies how many pixels to add vertically.
If :margin is not specified, the default is zero.
:ascent ascent:ascent property specifies the amount of the image's
height to use for its ascent—that is, the part above the baseline.
The value, ascent, must be a number in the range 0 to 100, or
the symbol center.
If ascent is a number, that percentage of the image's height is used for its ascent.
If ascent is center, the image is vertically centered
around a centerline which would be the vertical centerline of text drawn
at the position of the image, in the manner specified by the text
properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
:relief relief:relief property, if non-nil, adds a shadow rectangle
around the image. The value, relief, specifies the width of the
shadow lines, in pixels. If relief is negative, shadows are drawn
so that the image appears as a pressed button; otherwise, it appears as
an unpressed button.
:conversion algorithm:conversion property, if non-nil, specifies a
conversion algorithm that should be applied to the image before it is
displayed; the value, algorithm, specifies which algorithm.
laplaceemboss(edge-detection :matrix matrix :color-adjust adjust) (x-1/y-1 x/y-1 x+1/y-1
x-1/y x/y x+1/y
x-1/y+1 x/y+1 x+1/y+1)
The resulting pixel is computed from the color intensity of the color resulting from summing up the RGB values of surrounding pixels, multiplied by the specified factors, and dividing that sum by the sum of the factors' absolute values.
Laplace edge-detection currently uses a matrix of
(1 0 0
0 0 0
9 9 -1)
Emboss edge-detection uses a matrix of
( 2 -1 0
-1 0 1
0 1 -2)
disabled:mask maskheuristic or (heuristic bg), build
a clipping mask for the image, so that the background of a frame is
visible behind the image. If bg is not specified, or if bg
is t, determine the background color of the image by looking at
the four corners of the image, assuming the most frequently occurring
color from the corners is the background color of the image. Otherwise,
bg must be a list (red green blue)
specifying the color to assume for the background of the image.
If mask is nil, remove a mask from the image, if it has
one. Images in some formats include a mask which can be removed by
specifying :mask nil.
:pointer shape:map mapAn image map is an alist where each element has the format
(area id plist). An area is specified
as either a rectangle, a circle, or a polygon.
A rectangle is a cons
(rect . ((x0 . y0) . (x1 . y1)))
which specifies the pixel coordinates of the upper left and bottom right
corners of the rectangle area.
A circle is a cons
(circle . ((x0 . y0) . r))
which specifies the center and the radius of the circle; r may
be a float or integer.
A polygon is a cons
(poly . [x0 y0 x1 y1 ...])
where each pair in the vector describes one corner in the polygon.
When the mouse pointer lies on a hot-spot area of an image, the
plist of that hot-spot is consulted; if it contains a help-echo
property, that defines a tool-tip for the hot-spot, and if it contains
a pointer property, that defines the shape of the mouse cursor when
it is on the hot-spot.
See Pointer Shape, for available pointer shapes.
When you click the mouse when the mouse pointer is over a hot-spot, an
event is composed by combining the id of the hot-spot with the
mouse event; for instance, [area4 mouse-1] if the hot-spot's
id is area4.
This function returns
tif image spec has a mask bitmap. frame is the frame on which the image will be displayed. framenilor omitted means to use the selected frame (see Input Focus).
To use XBM format, specify xbm as the image type. This image
format doesn't require an external library, so images of this type are
always supported.
Additional image properties supported for the xbm image type are:
:foreground foregroundnil for the default color. This color is
used for each pixel in the XBM that is 1. The default is the frame's
foreground color.
:background backgroundnil for the default color. This color is
used for each pixel in the XBM that is 0. The default is the frame's
background color.
If you specify an XBM image using data within Emacs instead of an external file, use the following three properties:
:data data:height and :width.
:height and :width in this case,
because omitting them is what indicates the data has the format of an
XBM file. The file contents specify the height and width of the image.
height bits. In this case, you must specify
:height and :width, both to indicate that the string
contains just the bits rather than a whole XBM file, and to specify the
size of the image.
:width width:height height
To use XPM format, specify xpm as the image type. The
additional image property :color-symbols is also meaningful with
the xpm image type:
:color-symbols symbols(name . color). In each element, name is
the name of a color as it appears in the image file, and color
specifies the actual color to use for displaying that name.
For GIF images, specify image type gif.
:index index:index to specify one image from a GIF file that
contains more than one image. This property specifies use of image
number index from the file. If the GIF file doesn't contain an
image with index index, the image displays as a hollow box.
For TIFF images, specify image type tiff.
:index index:index to specify one image from a TIFF file that
contains more than one image. This property specifies use of image
number index from the file. If the TIFF file doesn't contain an
image with index index, the image displays as a hollow box.
To use PostScript for an image, specify image type postscript.
This works only if you have Ghostscript installed. You must always use
these three properties:
:pt-width width:pt-height height:bounding-box box%%BoundingBox: 22 171 567 738
For PBM images, specify image type pbm. Color, gray-scale and
monochromatic images are supported. For mono PBM images, two additional
image properties are supported.
:foreground foregroundnil for the default color. This color is
used for each pixel in the PBM that is 1. The default is the frame's
foreground color.
:background backgroundnil for the default color. This color is
used for each pixel in the PBM that is 0. The default is the frame's
background color.
For JPEG images, specify image type jpeg.
For TIFF images, specify image type tiff.
For PNG images, specify image type png.
For SVG images, specify image type svg.
The functions create-image, defimage and
find-image provide convenient ways to create image descriptors.
This function creates and returns an image descriptor which uses the data in file-or-data. file-or-data can be a file name or a string containing the image data; data-p should be
nilfor the former case, non-nilfor the latter case.The optional argument type is a symbol specifying the image type. If type is omitted or
nil,create-imagetries to determine the image type from the file's first few bytes, or else from the file's name.The remaining arguments, props, specify additional image properties—for example,
(create-image "foo.xpm" 'xpm nil :heuristic-mask t)The function returns
nilif images of this type are not supported. Otherwise it returns an image descriptor.
This macro defines symbol as an image name. The arguments specs is a list which specifies how to display the image. The third argument, doc, is an optional documentation string.
Each argument in specs has the form of a property list, and each one should specify at least the
:typeproperty and either the:fileor the:dataproperty. The value of:typeshould be a symbol specifying the image type, the value of:fileis the file to load the image from, and the value of:datais a string containing the actual image data. Here is an example:(defimage test-image ((:type xpm :file "~/test1.xpm") (:type xbm :file "~/test1.xbm")))
defimagetests each argument, one by one, to see if it is usable—that is, if the type is supported and the file exists. The first usable argument is used to make an image descriptor which is stored in symbol.If none of the alternatives will work, then symbol is defined as
nil.
This function provides a convenient way to find an image satisfying one of a list of image specifications specs.
Each specification in specs is a property list with contents depending on image type. All specifications must at least contain the properties
:typetype and either:filefile or:dataDATA, where type is a symbol specifying the image type, e.g.xbm, file is the file to load the image from, and data is a string containing the actual image data. The first specification in the list whose type is supported, and file exists, is used to construct the image specification to be returned. If no specification is satisfied,nilis returned.The image is looked for in
image-load-path.
This variable's value is a list of locations in which to search for image files. If an element is a string or a variable symbol whose value is a string, the string is taken to be the name of a directory to search. If an element is a variable symbol whose value is a list, that is taken to be a list of directory names to search.
The default is to search in the images subdirectory of the directory specified by
data-directory, then the directory specified bydata-directory, and finally in the directories inload-path. Subdirectories are not automatically included in the search, so if you put an image file in a subdirectory, you have to supply the subdirectory name explicitly. For example, to find the image images/foo/bar.xpm withindata-directory, you should specify the image as follows:(defimage foo-image '((:type xpm :file "foo/bar.xpm")))
This function returns a suitable search path for images used by the Lisp package library.
The function searches for image first using
image-load-path, excludingdata-directory/images, and then inload-path, followed by a path suitable for library, which includes ../../etc/images and ../etc/images relative to the library file itself, and finally indata-directory/images.Then this function returns a list of directories which contains first the directory in which image was found, followed by the value of
load-path. If path is given, it is used instead ofload-path.If no-error is non-
niland a suitable path can't be found, don't signal an error. Instead, return a list of directories as before, except thatnilappears in place of the image directory.Here is an example that uses a common idiom to provide compatibility with versions of Emacs that lack the variable
image-load-path:(defvar image-load-path) ; shush compiler (let* ((load-path (image-load-path-for-library "mh-e" "mh-logo.xpm")) (image-load-path (cons (car load-path) (when (boundp 'image-load-path) image-load-path)))) (mh-tool-bar-folder-buttons-init))
You can use an image descriptor by setting up the display
property yourself, but it is easier to use the functions in this
section.
This function inserts image in the current buffer at point. The value image should be an image descriptor; it could be a value returned by
create-image, or the value of a symbol defined withdefimage. The argument string specifies the text to put in the buffer to hold the image. If it is omitted ornil,insert-imageuses" "by default.The argument area specifies whether to put the image in a margin. If it is
left-margin, the image appears in the left margin;right-marginspecifies the right margin. If area isnilor omitted, the image is displayed at point within the buffer's text.The argument slice specifies a slice of the image to insert. If slice is
nilor omitted the whole image is inserted. Otherwise, slice is a list(x y width height)which specifies the x and y positions and width and height of the image area to insert. Integer values are in units of pixels. A floating point number in the range 0.0–1.0 stands for that fraction of the width or height of the entire image.Internally, this function inserts string in the buffer, and gives it a
displayproperty which specifies image. See Display Property.
This function inserts image in the current buffer at point, like
insert-image, but splits the image into rowsxcols equally sized slices.
This function puts image image in front of pos in the current buffer. The argument pos should be an integer or a marker. It specifies the buffer position where the image should appear. The argument string specifies the text that should hold the image as an alternative to the default.
The argument image must be an image descriptor, perhaps returned by
create-imageor stored bydefimage.The argument area specifies whether to put the image in a margin. If it is
left-margin, the image appears in the left margin;right-marginspecifies the right margin. If area isnilor omitted, the image is displayed at point within the buffer's text.Internally, this function creates an overlay, and gives it a
before-stringproperty containing text that has adisplayproperty whose value is the image. (Whew!)
This function removes images in buffer between positions start and end. If buffer is omitted or
nil, images are removed from the current buffer.This removes only images that were put into buffer the way
put-imagedoes it, not images that were inserted withinsert-imageor in other ways.
This function returns the size of an image as a pair
(width.height). spec is an image specification. pixels non-nilmeans return sizes measured in pixels, otherwise return sizes measured in canonical character units (fractions of the width/height of the frame's default font). frame is the frame on which the image will be displayed. frame null or omitted means use the selected frame (see Input Focus).
This variable is used to define the maximum size of image that Emacs will load. Emacs will refuse to load (and display) any image that is larger than this limit.
If the value is an integer, it directly specifies the maximum image height and width, measured in pixels. If it is a floating point number, it specifies the maximum image height and width as a ratio to the frame height and width. If the value is non-numeric, there is no explicit limit on the size of images.
The purpose of this variable is to prevent unreasonably large images from accidentally being loaded into Emacs. It only takes effect the first time an image is loaded. Once an image is placed in the image cache, it can always be displayed, even if the value of max-image-size is subsequently changed (see Image Cache).
Emacs caches images so that it can display them again more
efficiently. When Emacs displays an image, it searches the image
cache for an existing image specification equal to the desired
specification. If a match is found, the image is displayed from the
cache; otherwise, Emacs loads the image normally.
Occasionally, you may need to tell Emacs to refresh the images
associated with a given image specification. For example, suppose you
display an image using a specification that contains a :file
property. The image is automatically cached, and subsequent displays
of that image, with the same image specification, will use the image
cache. If the image file changes in the meantime, Emacs would be
displaying the old version of the image. In such a situation, you can
“refresh” the image by calling image-refresh.
In Emacs' current implementation, each graphical terminal possesses an image cache, which is shared by all the frames on that terminal (see Multiple Terminals). Thus, refreshing an image in one frame also refreshes it in all other frames on the same terminal.
This function refreshes any images with image specifications
equalto spec on frame frame. If frame isnil, it defaults to the selected frame. If frame ist, the refresh is applied to all existing frames.
This function clears an image cache, removing all the images stored in it. If filter is omitted or
nil, it clears the cache for the selected frame. If filter is a frame, it clears the cache for that frame. If filter ist, all image caches are cleared. Otherwise, filter is taken to be a file name, and all images associated with that file name are removed from all image caches.
If an image in the image cache has not been displayed for a specified period of time, Emacs removes it from the cache and frees the associated memory.
This variable specifies the number of seconds an image can remain in the cache without being displayed. When an image is not displayed for this length of time, Emacs removes it from the image cache.
If the value is
nil, Emacs does not remove images from the cache except when you explicitly clear it. This mode can be useful for debugging.
The button package defines functions for inserting and manipulating clickable (with the mouse, or via keyboard commands) buttons in Emacs buffers, such as might be used for help hyper-links, etc. Emacs uses buttons for the hyper-links in help text and the like.
A button is essentially a set of properties attached (via text properties or overlays) to a region of text in an Emacs buffer. These properties are called button properties.
One of these properties (action) is a function, which will
be called when the user invokes it using the keyboard or the mouse.
The invoked function may then examine the button and use its other
properties as desired.
In some ways the Emacs button package duplicates functionality offered
by the widget package (see Introduction), but the button package has the advantage that it is
much faster, much smaller, and much simpler to use (for elisp
programmers—for users, the result is about the same). The extra
speed and space savings are useful mainly if you need to create many
buttons in a buffer (for instance an *Apropos* buffer uses
buttons to make entries clickable, and may contain many thousands of
entries).
Buttons have an associated list of properties defining their appearance and behavior, and other arbitrary properties may be used for application specific purposes. Some properties that have special meaning to the button package include:
actionignore,
which does nothing.
mouse-actionaction, and when present, will be used
instead of action for button invocations resulting from
mouse-clicks (instead of the user hitting <RET>). If not
present, mouse-clicks use action instead.
facebutton face.
mouse-facehighlight face.
keymapbutton-map, which defines <RET> and
<mouse-2> to invoke the button.
type:type keyword argument.
See Button Types.
help-echo"mouse-2, RET: Push this button".
follow-linkbuttonnil button property, which may be useful
in finding regions of text that comprise buttons (which is what the
standard button functions do).
There are other properties defined for the regions of text in a button, but these are not generally interesting for typical uses.
Every button has a button type, which defines default values for the button's properties. Button types are arranged in a hierarchy, with specialized types inheriting from more general types, so that it's easy to define special-purpose types of buttons for specific tasks.
Define a `button type' called name (a symbol). The remaining arguments form a sequence of property value pairs, specifying default property values for buttons with this type (a button's type may be set by giving it a
typeproperty when creating the button, using the:typekeyword argument).In addition, the keyword argument
:supertypemay be used to specify a button-type from which name inherits its default property values. Note that this inheritance happens only when name is defined; subsequent changes to a supertype are not reflected in its subtypes.
Using define-button-type to define default properties for
buttons is not necessary—buttons without any specified type use the
built-in button-type button—but it is encouraged, since
doing so usually makes the resulting code clearer and more efficient.
Buttons are associated with a region of text, using an overlay or
text properties to hold button-specific information, all of which are
initialized from the button's type (which defaults to the built-in
button type button). Like all Emacs text, the appearance of
the button is governed by the face property; by default (via
the face property inherited from the button button-type)
this is a simple underline, like a typical web-page link.
For convenience, there are two sorts of button-creation functions,
those that add button properties to an existing region of a buffer,
called make-...button, and those that also insert the button
text, called insert-...button.
The button-creation functions all take the &rest argument
properties, which should be a sequence of property value
pairs, specifying properties to add to the button; see Button Properties. In addition, the keyword argument :type may be
used to specify a button-type from which to inherit other properties;
see Button Types. Any properties not explicitly specified
during creation will be inherited from the button's type (if the type
defines such a property).
The following functions add a button using an overlay (see Overlays) to hold the button properties:
This makes a button from beg to end in the current buffer, and returns it.
This insert a button with the label label at point, and returns it.
The following functions are similar, but use Emacs text properties (see Text Properties) to hold the button properties, making the button actually part of the text instead of being a property of the buffer. Buttons using text properties do not create markers into the buffer, which is important for speed when you use extremely large numbers of buttons. (However, if there is an existing face text property at the site of the button, the button face may not be visible.) Both functions return the position of the start of the new button:
This makes a button from beg to end in the current buffer, using text properties.
This inserts a button with the label label at point, using text properties.
These are functions for getting and setting properties of buttons. Often these are used by a button's invocation function to determine what to do.
Where a button parameter is specified, it means an object referring to a specific button, either an overlay (for overlay buttons), or a buffer-position or marker (for text property buttons). Such an object is passed as the first argument to a button's invocation function when it is invoked.
Call button's
actionproperty (i.e., invoke it). If use-mouse-action is non-nil, try to invoke the button'smouse-actionproperty instead ofaction; if the button has nomouse-actionproperty, useactionas normal.
Return
tif button has button-type type, or one of type's subtypes.
Return
tif button-type type is a subtype of supertype.
These are commands and functions for locating and operating on buttons in an Emacs buffer.
push-button is the command that a user uses to actually `push'
a button, and is bound by default in the button itself to <RET>
and to <mouse-2> using a region-specific keymap. Commands
that are useful outside the buttons itself, such as
forward-button and backward-button are additionally
available in the keymap stored in button-buffer-map; a mode
which uses buttons may want to use button-buffer-map as a
parent keymap for its keymap.
If the button has a non-nil follow-link property, and
mouse-1-click-follows-link is set, a quick <Mouse-1> click
will also activate the push-button command.
See Clickable Text.
Perform the action specified by a button at location pos. pos may be either a buffer position or a mouse-event. If use-mouse-action is non-
nil, or pos is a mouse-event (see Mouse Events), try to invoke the button'smouse-actionproperty instead ofaction; if the button has nomouse-actionproperty, useactionas normal. pos defaults to point, except whenpush-buttonis invoked interactively as the result of a mouse-event, in which case, the mouse event's position is used. If there's no button at pos, do nothing and returnnil, otherwise returnt.
Move to the nth next button, or nth previous button if n is negative. If n is zero, move to the start of any button at point. If wrap is non-
nil, moving past either end of the buffer continues from the other end. If display-message is non-nil, the button's help-echo string is displayed. Any button with a non-nilskipproperty is skipped over. Returns the button found.
Move to the nth previous button, or nth next button if n is negative. If n is zero, move to the start of any button at point. If wrap is non-
nil, moving past either end of the buffer continues from the other end. If display-message is non-nil, the button's help-echo string is displayed. Any button with a non-nilskipproperty is skipped over. Returns the button found.
Return the next button after (for
next-buttonor before (forprevious-button) position pos in the current buffer. If count-current is non-nil, count any button at pos in the search, instead of starting at the next button.
The Ewoc package constructs buffer text that represents a structure of Lisp objects, and updates the text to follow changes in that structure. This is like the “view” component in the “model/view/controller” design paradigm.
An ewoc is a structure that organizes information required to construct buffer text that represents certain Lisp data. The buffer text of the ewoc has three parts, in order: first, fixed header text; next, textual descriptions of a series of data elements (Lisp objects that you specify); and last, fixed footer text. Specifically, an ewoc contains information on:
Typically, you define an ewoc with ewoc-create, and then pass
the resulting ewoc structure to other functions in the Ewoc package to
build nodes within it, and display it in the buffer. Once it is
displayed in the buffer, other functions determine the correspondance
between buffer positions and nodes, move point from one node's textual
representation to another, and so forth. See Abstract Display Functions.
A node encapsulates a data element much the way a variable holds a value. Normally, encapsulation occurs as a part of adding a node to the ewoc. You can retrieve the data element value and place a new value in its place, like so:
(ewoc-data node)
⇒ value
(ewoc-set-data node new-value)
⇒ new-value
You can also use, as the data element value, a Lisp object (list or vector) that is a container for the “real” value, or an index into some other structure. The example (see Abstract Display Example) uses the latter approach.
When the data changes, you will want to update the text in the
buffer. You can update all nodes by calling ewoc-refresh, or
just specific nodes using ewoc-invalidate, or all nodes
satisfying a predicate using ewoc-map. Alternatively, you can
delete invalid nodes using ewoc-delete or ewoc-filter,
and add new nodes in their place. Deleting a node from an ewoc deletes
its associated textual description from buffer, as well.
In this subsection, ewoc and node stand for the structures described above (see Abstract Display), while data stands for an arbitrary Lisp object used as a data element.
This constructs and returns a new ewoc, with no nodes (and thus no data elements). pretty-printer should be a function that takes one argument, a data element of the sort you plan to use in this ewoc, and inserts its textual description at point using
insert(and neverinsert-before-markers, because that would interfere with the Ewoc package's internal mechanisms).Normally, a newline is automatically inserted after the header, the footer and every node's textual description. If nosep is non-
nil, no newline is inserted. This may be useful for displaying an entire ewoc on a single line, for example, or for making nodes “invisible” by arranging for pretty-printer to do nothing for those nodes.An ewoc maintains its text in the buffer that is current when you create it, so switch to the intended buffer before calling
ewoc-create.
This returns a cons cell
(header.footer)made from ewoc's header and footer.
This sets the header and footer of ewoc to the strings header and footer, respectively.
These add a new node encapsulating data, putting it, respectively, at the beginning or end of ewoc's chain of nodes.
These add a new node encapsulating data, adding it to ewoc before or after node, respectively.
These return, respectively, the previous node and the next node of node in ewoc.
This returns the node in ewoc found at zero-based index n. A negative n means count from the end.
ewoc-nthreturnsnilif n is out of range.
This determines the node in ewoc which contains point (or pos if specified), and returns that node. If ewoc has no nodes, it returns
nil. If pos is before the first node, it returns the first node; if pos is after the last node, it returns the last node. The optional third arg guess should be a node that is likely to be near pos; this doesn't alter the result, but makes the function run faster.
These move point to the previous or next, respectively, argth node in ewoc.
ewoc-goto-prevdoes not move if it is already at the first node or if ewoc is empty, whereasewoc-goto-nextmoves past the last node, returningnil. Excepting this special case, these functions return the node moved to.
This function regenerates the text of ewoc. It works by deleting the text between the header and the footer, i.e., all the data elements' representations, and then calling the pretty-printer function for each node, one by one, in order.
This is similar to
ewoc-refresh, except that only nodes in ewoc are updated instead of the entire set.
This calls predicate for each data element in ewoc and deletes those nodes for which predicate returns
nil. Any args are passed to predicate.
This calls predicate for each data element in ewoc and returns a list of those elements for which predicate returns non-
nil. The elements in the list are ordered as in the buffer. Any args are passed to predicate.
This calls map-function for each data element in ewoc and updates those nodes for which map-function returns non-
nil. Any args are passed to map-function.
Here is a simple example using functions of the ewoc package to implement a “color components display,” an area in a buffer that represents a vector of three integers (itself representing a 24-bit RGB value) in various ways.
(setq colorcomp-ewoc nil
colorcomp-data nil
colorcomp-mode-map nil
colorcomp-labels ["Red" "Green" "Blue"])
(defun colorcomp-pp (data)
(if data
(let ((comp (aref colorcomp-data data)))
(insert (aref colorcomp-labels data) "\t: #x"
(format "%02X" comp) " "
(make-string (ash comp -2) ?#) "\n"))
(let ((cstr (format "#%02X%02X%02X"
(aref colorcomp-data 0)
(aref colorcomp-data 1)
(aref colorcomp-data 2)))
(samp " (sample text) "))
(insert "Color\t: "
(propertize samp 'face `(foreground-color . ,cstr))
(propertize samp 'face `(background-color . ,cstr))
"\n"))))
(defun colorcomp (color)
"Allow fiddling with COLOR in a new buffer.
The buffer is in Color Components mode."
(interactive "sColor (name or #RGB or #RRGGBB): ")
(when (string= "" color)
(setq color "green"))
(unless (color-values color)
(error "No such color: %S" color))
(switch-to-buffer
(generate-new-buffer (format "originally: %s" color)))
(kill-all-local-variables)
(setq major-mode 'colorcomp-mode
mode-name "Color Components")
(use-local-map colorcomp-mode-map)
(erase-buffer)
(buffer-disable-undo)
(let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
(color-values color))))
(ewoc (ewoc-create 'colorcomp-pp
"\nColor Components\n\n"
(substitute-command-keys
"\n\\{colorcomp-mode-map}"))))
(set (make-local-variable 'colorcomp-data) data)
(set (make-local-variable 'colorcomp-ewoc) ewoc)
(ewoc-enter-last ewoc 0)
(ewoc-enter-last ewoc 1)
(ewoc-enter-last ewoc 2)
(ewoc-enter-last ewoc nil)))
This example can be extended to be a “color selection widget” (in
other words, the controller part of the “model/view/controller”
design paradigm) by defining commands to modify colorcomp-data
and to “finish” the selection process, and a keymap to tie it all
together conveniently.
(defun colorcomp-mod (index limit delta)
(let ((cur (aref colorcomp-data index)))
(unless (= limit cur)
(aset colorcomp-data index (+ cur delta)))
(ewoc-invalidate
colorcomp-ewoc
(ewoc-nth colorcomp-ewoc index)
(ewoc-nth colorcomp-ewoc -1))))
(defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
(defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
(defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
(defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
(defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
(defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
(defun colorcomp-copy-as-kill-and-exit ()
"Copy the color components into the kill ring and kill the buffer.
The string is formatted #RRGGBB (hash followed by six hex digits)."
(interactive)
(kill-new (format "#%02X%02X%02X"
(aref colorcomp-data 0)
(aref colorcomp-data 1)
(aref colorcomp-data 2)))
(kill-buffer nil))
(setq colorcomp-mode-map
(let ((m (make-sparse-keymap)))
(suppress-keymap m)
(define-key m "i" 'colorcomp-R-less)
(define-key m "o" 'colorcomp-R-more)
(define-key m "k" 'colorcomp-G-less)
(define-key m "l" 'colorcomp-G-more)
(define-key m "," 'colorcomp-B-less)
(define-key m "." 'colorcomp-B-more)
(define-key m " " 'colorcomp-copy-as-kill-and-exit)
m))
Note that we never modify the data in each node, which is fixed when the
ewoc is created to be either nil or an index into the vector
colorcomp-data, the actual color components.
This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.
The value of this variable should be a function (of no arguments) to be called whenever a character with close parenthesis syntax is inserted. The value of
blink-paren-functionmay benil, in which case nothing is done.
This variable specifies the maximum distance to scan for a matching parenthesis before giving up.
This variable specifies the number of seconds for the cursor to remain at the matching parenthesis. A fraction of a second often gives good results, but the default is 1, which works on all systems.
This function is the default value of
blink-paren-function. It assumes that point follows a character with close parenthesis syntax and moves the cursor momentarily to the matching opening character. If that character is not already on the screen, it displays the character's context in the echo area. To avoid long delays, this function does not search farther thanblink-matching-paren-distancecharacters.Here is an example of calling this function explicitly.
(defun interactive-blink-matching-open () "Indicate momentarily the start of sexp before point." (interactive) (let ((blink-matching-paren-distance (buffer-size)) (blink-matching-paren t)) (blink-matching-open)))
The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (see Display Tables). Here are the usual display conventions:
tab-width.
ctl-arrow. If it is
non-nil, these codes map to sequences of two glyphs, where the
first glyph is the ASCII code for ‘^’. (A display table can
specify a glyph to use instead of ‘^’.) Otherwise, these codes map
just like the codes in the range 128 to 255.
On MS-DOS terminals, Emacs arranges by default for the character code 127 to be mapped to the glyph code 127, which normally displays as an empty polygon. This glyph is used to display non-ASCII characters that the MS-DOS terminal doesn't support. See MS-DOS and MULE.
The usual display conventions apply even when there is a display
table, for any character whose entry in the active display table is
nil. Thus, when you set up a display table, you need only
specify the characters for which you want special behavior.
These display rules apply to carriage return (character code 13), when it appears in the buffer. But that character may not appear in the buffer where you expect it, if it was eliminated as part of end-of-line conversion (see Coding System Basics).
These variables affect the way certain characters are displayed on the
screen. Since they change the number of columns the characters occupy,
they also affect the indentation functions. These variables also affect
how the mode line is displayed; if you want to force redisplay of the
mode line using the new values, call the function
force-mode-line-update (see Mode Line Format).
This buffer-local variable controls how control characters are displayed. If it is non-
nil, they are displayed as a caret followed by the character: ‘^A’. If it isnil, they are displayed as a backslash followed by three octal digits: ‘\001’.
The value of this buffer-local variable is the spacing between tab stops used for displaying tab characters in Emacs buffers. The value is in units of columns, and the default is 8. Note that this feature is completely independent of the user-settable tab stops used by the command
tab-to-tab-stop. See Indent Tabs.
You can use the display table feature to control how all possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ASCII character set.
The display table maps each character code into a sequence of glyphs, each glyph being a graphic that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the glyph table.
Display tables affect how the mode line is displayed; if you want to
force redisplay of the mode line using a new display table, call
force-mode-line-update (see Mode Line Format).
A display table is actually a char-table (see Char-Tables) with
display-table as its subtype.
This creates and returns a display table. The table initially has
nilin all elements.
The ordinary elements of the display table are indexed by character
codes; the element at index c says how to display the character
code c. The value should be nil or a vector of the
glyphs to be output (see Glyphs). nil says to display the
character c according to the usual display conventions
(see Usual Display).
Warning: if you use the display table to change the display of newline characters, the whole buffer will be displayed as one long “line.”
The display table also has six “extra slots” which serve special
purposes. Here is a table of their meanings; nil in any slot
means to use the default for that slot, as stated below.
For example, here is how to construct a display table that mimics the
effect of setting ctl-arrow to a non-nil value:
(setq disptab (make-display-table))
(let ((i 0))
(while (< i 32)
(or (= i ?\t) (= i ?\n)
(aset disptab i (vector ?^ (+ i 64))))
(setq i (1+ i)))
(aset disptab 127 (vector ?^ ??)))
This function returns the value of the extra slot slot of display-table. The argument slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols are
truncation,wrap,escape,control,selective-display, andvertical-border.
This function stores value in the extra slot slot of display-table. The argument slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols are
truncation,wrap,escape,control,selective-display, andvertical-border.
This function displays a description of the display table display-table in a help buffer.
This command displays a description of the current display table in a help buffer.
Each window can specify a display table, and so can each buffer. When a buffer b is displayed in window w, display uses the display table for window w if it has one; otherwise, the display table for buffer b if it has one; otherwise, the standard display table if any. The display table chosen is called the active display table.
This function returns window's display table, or
nilif window does not have an assigned display table. The default for window is the selected window.
This function sets the display table of window to table. The argument table should be either a display table or
nil.
This variable is automatically buffer-local in all buffers; its value in a particular buffer specifies the display table for that buffer. If it is
nil, that means the buffer does not have an assigned display table.
This variable's value is the default display table, used whenever a window has no display table and neither does the buffer displayed in that window. This variable is
nilby default.
If there is no display table to use for a particular window—that is,
if the window specifies none, its buffer specifies none, and
standard-display-table is nil—then Emacs uses the usual
display conventions for all character codes in that window. See Usual Display.
A number of functions for changing the standard display table are defined in the library disp-table.
A glyph is a generalization of a character; it stands for an image that takes up a single character position on the screen. Normally glyphs come from vectors in the display table (see Display Tables).
A glyph is represented in Lisp as a glyph code. A glyph code can be simple or it can be defined by the glyph table. A simple glyph code is just a way of specifying a character and a face to output it in. See Faces.
The following functions are used to manipulate simple glyph codes:
This function returns a simple glyph code representing char char with face face.
This function returns face of simple glyph code glyph, or
nilif glyph has the default face (face-id 0). See Face Functions.
On character terminals, you can set up a glyph table to define the meaning of glyph codes (represented as small integers).
The value of this variable is the current glyph table. It should be
nilor a vector whose gth element defines glyph code g.If a glyph code is greater than or equal to the length of the glyph table, that code is automatically simple. If
glyph-tableisnilthen all glyph codes are simple.The glyph table is used only on character terminals. On graphical displays, all glyph codes are simple.
Here are the meaningful types of elements in the glyph table:
make-glyph-code. You can use such an alias to define a
small-numbered glyph code which specifies a character with a face.
nilThis function returns a newly-allocated glyph code which is set up to display by sending string to the terminal.
This section describes how to make Emacs ring the bell (or blink the screen) to attract the user's attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use just beeping when signaling an error is more appropriate. (See Errors.)
This function beeps, or flashes the screen (see
visible-bellbelow). It also terminates any keyboard macro currently executing unless do-not-terminate is non-nil.
This variable determines whether Emacs should flash the screen to represent a bell. Non-
nilmeans yes,nilmeans no. This is effective on graphical displays, and on text-only terminals provided the terminal's Termcap entry defines the visible bell capability (‘vb’).
If this is non-
nil, it specifies how Emacs should “ring the bell.” Its value should be a function of no arguments. If this is non-nil, it takes precedence over thevisible-bellvariable.
Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term “window,” but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.
This frame-local variable tells Lisp programs what window system Emacs is using for displaying the frame. The possible values are
x- Emacs is displaying the frame using X.
w32- Emacs is displaying the frame using native MS-Windows GUI.
ns- Emacs is displaying the frame using the Nextstep interface (used on GNUstep and Mac OS X).
pc- Emacs is displaying the frame using MS-DOS direct screen writes.
nil- Emacs is displaying the frame on a character-based terminal.
This variable holds the value of
window-systemused for the first frame created by Emacs during startup. (When Emacs is invoked with the --daemon option, it does not create any initial frames, soinitial-window-systemisnil. See daemon.)
This function returns a symbol whose name tells what window system is used for displaying frame (which defaults to the currently selected frame). The list of possible symbols it returns is the same one documented for the variable
window-systemabove.
Do not use window-system and
initial-window-system as predicates or boolean flag variables,
if you want to write code that works differently on text terminals and
graphic displays. That is because window-system is not a good
indicator of Emacs capabilities on a given display type. Instead, use
display-graphic-p or any of the other display-*-p
predicates described in Display Feature Testing.
This variable is a normal hook which Emacs runs after handling the initialization files. Emacs runs this hook after it has completed loading your init file, the default initialization file (if any), and the terminal-specific Lisp code, and running the hook
term-setup-hook.This hook is used for internal purposes: setting up communication with the window system, and creating the initial window. Users should not interfere with it.
This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output, and flow control.
See Building Emacs, for related information. See Display, for additional operating system status information pertaining to the terminal and the screen.
This section describes what Emacs does when it is started, and how you can customize these actions.
When Emacs is started up, it performs the following operations (which are defined in startup.el):
load-path, by running the file named
subdirs.el in each directory in the list. Normally, this file
adds the directory's subdirectories to the list, and those are scanned
in their turn. The files subdirs.el are normally generated
automatically when Emacs is installed.
before-init-time to the value of
current-time (see Time of Day). It also sets
after-init-time to nil, which signals to Lisp programs
that Emacs is being initialized.
initial-window-system (see initial-window-system). This library's name is
term/windowsystem-win.el, where windowsystem is the
value of initial-window-system. From that library, it calls
the appropriate initialization function. The initialization function
for each supported window system is specified by
window-system-initialization-alist.
LANG.
before-init-hook.
inhibit-default-init is non-nil, nor if the options
‘-q’, ‘-Q’, or ‘--batch’ were specified.
abbrev-file-name, if that file exists and can be read
(see abbrev-file-name). This is not done if the
option ‘--batch’ was specified.
after-init-time to the value of
current-time. This variable was set to nil earlier;
setting it to the current time signals that the initialization phase
is over, and, together with before-init-time, provides the
measurement of how long it took.
after-init-hook.
initial-major-mode.
term-file-prefix (see Terminal-Specific). This is not done
in --batch mode, nor if term-file-prefix is nil.
inhibit-startup-echo-area-message.
--batch was specified.
initial-buffer-choice is a string, it visits the file with
that name. Furthermore, if the ‘*scratch*’ buffer exists and is
empty, it inserts initial-scratch-message into that buffer.
emacs-startup-hook and then term-setup-hook.
frame-notice-user-settings, which modifies the
parameters of the selected frame according to whatever the init files
specify.
window-setup-hook. See Window Systems.
--daemon was specified, it calls
server-start and detaches from the controlling terminal.
See Emacs Server.
initial-buffer-choice or
inhibit-startup-screen are nil, nor if the
‘--no-splash’ or ‘-Q’ command-line options were specified.
emacs-session-restore passing it as argument the ID of the
previous session. See Session Management.
This variable, if non-
nil, inhibits the startup screen. In that case, Emacs typically displays the ‘*scratch*’ buffer; but seeinitial-buffer-choice, below.Do not set this variable in the init file of a new user, or in a way that affects more than one user, as that would prevent new users from receiving information about copyleft and basic Emacs usage.
inhibit-startup-messageandinhibit-splash-screenare aliases for this variable.
This variable, if non-
nil, determines a file or buffer for Emacs to display after starting up, instead of the startup screen. If its value ist, Emacs displays the ‘*scratch*’ buffer. If its value is a string, that specifies the name of a file for Emacs to visit.
This variable controls the display of the startup echo area message. You can suppress the startup echo area message by adding text with this form to your init file:
(setq inhibit-startup-echo-area-message "your-login-name")Emacs explicitly checks for an expression as shown above in your init file; your login name must appear in the expression as a Lisp string constant. Other methods of setting
inhibit-startup-echo-area-messageto the same value do not inhibit the startup message. This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your init file will not inhibit the message for someone else.
This variable, if non-
nil, should be a string, which is inserted into the ‘*scratch*’ buffer when Emacs starts up. If it isnil, the ‘*scratch*’ buffer is empty.
When you start Emacs, it normally attempts to load your init file. This is either a file named .emacs or .emacs.el in your home directory, or a file named init.el in a subdirectory named .emacs.d in your home directory. Whichever place you use, you can also compile the file (see Byte Compilation); then the actual file loaded will be .emacs.elc or init.elc.
The command-line switches ‘-q’, ‘-Q’, and ‘-u’
control whether and where to find the init file; ‘-q’ (and the
stronger ‘-Q’) says not to load an init file, while ‘-u
user’ says to load user's init file instead of yours.
See Entering Emacs. If neither
option is specified, Emacs uses the LOGNAME environment
variable, or the USER (most systems) or USERNAME (MS
systems) variable, to find your home directory and thus your init
file; this way, even if you have su'd, Emacs still loads your own init
file. If those environment variables are absent, though, Emacs uses
your user-id to find your home directory.
A site may have a default init file, which is the library
named default.el. Emacs finds the default.el file
through the standard search path for libraries (see How Programs Do Loading). The Emacs distribution does not come with this file; sites
may provide one for local customizations. If the default init file
exists, it is loaded whenever you start Emacs, except in batch mode or
if ‘-q’ (or ‘-Q’) is specified. But your own personal init
file, if any, is loaded first; if it sets inhibit-default-init
to a non-nil value, then Emacs does not subsequently load the
default.el file.
Another file for site-customization is site-start.el. Emacs loads this before the user's init file. You can inhibit the loading of this file with the option ‘--no-site-file’.
This variable specifies the site-customization file to load before the user's init file. Its normal value is
"site-start". The only way you can change it with real effect is to do so before dumping Emacs.
See Init File Examples, for examples of how to make various commonly desired customizations in your .emacs file.
This variable prevents Emacs from loading the default initialization library file for your session of Emacs. If its value is non-
nil, then the default library is not loaded. The default value isnil.
This normal hook is run, once, just before loading all the init files (the user's init file, default.el, and/or site-start.el). (The only way to change it with real effect is before dumping Emacs.)
This normal hook is run, once, just after loading all the init files (the user's init file, default.el, and/or site-start.el), before loading the terminal-specific library and processing the command-line action arguments.
This normal hook is run, once, just after handling the command line arguments, just before
term-setup-hook.
This variable holds the absolute file name of the user's init file. If the actual init file loaded is a compiled file, such as .emacs.elc, the value refers to the corresponding source file.
This variable holds the name of the .emacs.d directory. It is ordinarily ~/.emacs.d, but differs on some platforms.
Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal. The library's name is constructed by
concatenating the value of the variable term-file-prefix and the
terminal type (specified by the environment variable TERM).
Normally, term-file-prefix has the value
"term/"; changing this is not recommended. Emacs finds the file
in the normal manner, by searching the load-path directories, and
trying the ‘.elc’ and ‘.el’ suffixes.
The usual function of a terminal-specific library is to enable
special keys to send sequences that Emacs can recognize. It may also
need to set or add to input-decode-map if the Termcap or
Terminfo entry does not specify all the terminal's function keys.
See Terminal Input.
When the name of the terminal type contains a hyphen, and no library
is found whose name is identical to the terminal's name, Emacs strips
from the terminal's name the last hyphen and everything that follows
it, and tries again. This process is repeated until Emacs finds a
matching library or until there are no more hyphens in the name (the
latter means the terminal doesn't have any library specific to it).
Thus, for example, if there are no ‘aaa-48’ and ‘aaa-30’
libraries, Emacs will try the same library term/aaa.el for
terminal types ‘aaa-48’ and ‘aaa-30-rv’. If necessary, the
library can evaluate (getenv "TERM") to find the full name of
the terminal type.
Your init file can prevent the loading of the
terminal-specific library by setting the variable
term-file-prefix to nil. This feature is useful when
experimenting with your own peculiar customizations.
You can also arrange to override some of the actions of the
terminal-specific library by setting the variable
term-setup-hook. This is a normal hook which Emacs runs using
run-hooks at the end of Emacs initialization, after loading both
your init file and any terminal-specific libraries. You can
use this variable to define initializations for terminals that do not
have their own libraries. See Hooks.
If the
term-file-prefixvariable is non-nil, Emacs loads a terminal-specific initialization file as follows:(load (concat term-file-prefix (getenv "TERM")))You may set the
term-file-prefixvariable tonilin your init file if you do not wish to load the terminal-initialization file. To do this, put the following in your init file:(setq term-file-prefix nil).On MS-DOS, if the environment variable
TERMis not set, Emacs uses ‘internal’ as the terminal type.
This variable is a normal hook that Emacs runs after loading your init file, the default initialization file (if any) and the terminal-specific Lisp file.
You can use
term-setup-hookto override the definitions made by a terminal-specific file.
See window-setup-hook in Window Systems, for a related
feature.
You can use command-line arguments to request various actions when you start Emacs. Since you do not need to start Emacs more than once per day, and will often leave your Emacs session running longer than that, command-line arguments are hardly ever used. As a practical matter, it is best to avoid making the habit of using them, since this habit would encourage you to kill and restart Emacs unnecessarily often. These options exist for two reasons: to be compatible with other editors (for invocation by other programs) and to enable shell scripts to run specific Lisp programs.
This section describes how Emacs processes command-line arguments, and how you can customize them.
This function parses the command line that Emacs was called with, processes it, loads the user's init file and displays the startup messages.
The value of this variable is
tonce the command line has been processed.If you redump Emacs by calling
dump-emacs, you may wish to set this variable tonilfirst in order to cause the new dumped Emacs to process its new command-line arguments.
The value of this variable is an alist of user-defined command-line options and associated handler functions. This variable exists so you can add elements to it.
A command-line option is an argument on the command line, which has the form:
-optionThe elements of the
command-switch-alistlook like this:(option . handler-function)The car, option, is a string, the name of a command-line option (not including the initial hyphen). The handler-function is called to handle option, and receives the option name as its sole argument.
In some cases, the option is followed in the command line by an argument. In these cases, the handler-function can find all the remaining command-line arguments in the variable
command-line-args-left. (The entire list of command-line arguments is incommand-line-args.)The command-line arguments are parsed by the
command-line-1function in the startup.el file. See also Command Line Arguments for Emacs Invocation.
The value of this variable is the list of command-line arguments passed to Emacs.
The value of this variable is the list of command-line arguments that have not yet been processed.
argvis an alias for this.
This variable's value is a list of functions for handling an unrecognized command-line argument. Each time the next argument to be processed has no special meaning, the functions in this list are called, in order of appearance, until one of them returns a non-
nilvalue.These functions are called with no arguments. They can access the command-line argument under consideration through the variable
argi, which is bound temporarily at this point. The remaining arguments (not including the current one) are in the variablecommand-line-args-left.When a function recognizes and processes the argument in
argi, it should return a non-nilvalue to say it has dealt with that argument. If it has also dealt with some of the following arguments, it can indicate that by deleting them fromcommand-line-args-left.If all of these functions return
nil, then the argument is used as a file name to visit.
There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. As a practical matter, you seldom kill Emacs—only when you are about to log out. Suspending is much more common.
Killing Emacs means ending the execution of the Emacs process. The
parent process normally resumes control. The low-level primitive for
killing Emacs is kill-emacs.
This command exits the Emacs process and kills it.
If exit-data is an integer, then it is used as the exit status of the Emacs process. (This is useful primarily in batch operation; see Batch Mode.)
If exit-data is a string, its contents are stuffed into the terminal input buffer so that the shell (or whatever program next reads input) can read them.
All the information in the Emacs process, aside from files that have
been saved, is lost when the Emacs process is killed. Because killing
Emacs inadvertently can lose a lot of work, Emacs queries for
confirmation before actually terminating if you have buffers that need
saving or subprocesses that are running. This is done in the function
save-buffers-kill-emacs, the higher level function from which
kill-emacs is usually called.
After asking the standard questions,
save-buffers-kill-emacscalls the functions in the listkill-emacs-query-functions, in order of appearance, with no arguments. These functions can ask for additional confirmation from the user. If any of them returnsnil,save-buffers-kill-emacsdoes not kill Emacs, and does not run the remaining functions in this hook. Callingkill-emacsdirectly does not run this hook.
This variable is a normal hook; once
save-buffers-kill-emacsis finished with all file saving and confirmation, it callskill-emacswhich runs the functions in this hook.kill-emacsdoes not run this hook in batch mode.
kill-emacsmay be invoked directly (that is not viasave-buffers-kill-emacs) if the terminal is disconnected, or in similar situations where interaction with the user is not possible. Thus, if your hook needs to interact with the user, put it onkill-emacs-query-functions; if it needs to run regardless of how Emacs is killed, put it onkill-emacs-hook.
On text-only terminals, it is possible to suspend Emacs, which
means stopping Emacs temporarily and returning control to its superior
process, which is usually the shell. This allows you to resume
editing later in the same Emacs process, with the same buffers, the
same kill ring, the same undo history, and so on. To resume Emacs,
use the appropriate command in the parent shell—most likely
fg.
Suspending works only on a terminal device from which the Emacs session was started. We call that device the controlling terminal of the session. Suspending is not allowed if the controlling terminal is a graphical terminal.
Some operating systems do not support suspension of jobs; on these systems, “suspension” actually creates a new shell temporarily as a subprocess of Emacs. Then you would exit the shell to return to Emacs.
This function stops Emacs and returns control to the superior process. If and when the superior process resumes Emacs,
suspend-emacsreturnsnilto its caller in Lisp.This function works only on the controlling terminal of the Emacs session; to relinquish control of other tty devices, use
suspend-tty(see below). If the Emacs session uses more than one terminal, you must delete the frames on all the other terminals before suspending Emacs, or this function signals an error. See Multiple Terminals.If string is non-
nil, its characters are sent to Emacs's superior shell, to be read as terminal input. The characters in string are not echoed by the superior shell; only the results appear.Before suspending,
suspend-emacsruns the normal hooksuspend-hook. After the user resumes Emacs,suspend-emacsruns the normal hooksuspend-resume-hook. See Hooks.The next redisplay after resumption will redraw the entire screen, unless the variable
no-redraw-on-reenteris non-nil. See Refresh Screen.In the following example, note that ‘pwd’ is not echoed after Emacs is suspended. But it is read and executed by the shell.
(suspend-emacs) ⇒ nil (add-hook 'suspend-hook (function (lambda () (or (y-or-n-p "Really suspend? ") (error "Suspend canceled"))))) ⇒ (lambda nil (or (y-or-n-p "Really suspend? ") (error "Suspend canceled"))) (add-hook 'suspend-resume-hook (function (lambda () (message "Resumed!")))) ⇒ (lambda nil (message "Resumed!")) (suspend-emacs "pwd") ⇒ nil ---------- Buffer: Minibuffer ---------- Really suspend? y ---------- Buffer: Minibuffer ---------- ---------- Parent Shell ---------- lewis@slug[23] % /user/lewis/manual lewis@slug[24] % fg ---------- Echo Area ---------- Resumed!
This variable is a normal hook that Emacs runs on resuming after a suspension.
If tty specifies a terminal device used by Emacs, this function relinquishes the device and restores it to its prior state. Frames that used the device continue to exist, but are not updated and Emacs doesn't read input from them. tty can be a terminal object, a frame (meaning the terminal for that frame), or
nil(meaning the terminal for the selected frame). See Multiple Terminals.If tty is already suspended, this function does nothing.
This function runs the hook
suspend-tty-functions, passing the terminal object as an argument to each function.
This function resumes the previously suspended terminal device tty; tty can be a terminal object, a frame (meaning the terminal for that frame), or
nil(meaning the terminal for the selected frame).This function reopens the terminal device, re-initializes it, and redraws its with that terminal's selected frame. It then runs the hook
resume-tty-functions, passing the terminal object as an argument to each function.If the same device is already used by another Emacs terminal, this function signals an error.
This function returns non-
nilif terminal is the controlling terminal of the Emacs session;terminalcan be a terminal object, a frame (meaning the terminal for that frame), ornil(meaning the terminal for the selected frame).
This command suspends a frame. For GUI frames, it calls
iconify-frame(see Visibility of Frames); for text-only frames, it calls eithersuspend-emacsorsuspend-tty, depending on whether the frame is displayed on the controlling terminal device or not.
Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's UID, and so on.
This variable holds the standard GNU configuration name for the hardware/software configuration of your system, as a string. The convenient way to test parts of this string is with
string-match.
The value of this variable is a symbol indicating the type of operating system Emacs is operating on. Here is a table of the possible values:
aix- IBM's AIX.
berkeley-unix- Berkeley BSD and its variants.
cygwin- Cygwin, a Posix layer on top of MS-Windows.
darwin- Darwin (Mac OS X).
gnu- The GNU system (using the GNU kernel, which consists of the HURD and Mach).
gnu/linux- A GNU/Linux system—that is, a variant GNU system, using the Linux kernel. (These systems are the ones people often call “Linux,” but actually Linux is just the kernel, not the whole system.)
gnu/kfreebsd- A GNU (glibc-based) system with a FreeBSD kernel.
hpux- Hewlett-Packard HPUX operating system.
irix- Silicon Graphics Irix system.
lynxos 3.0.1- LynxOS-3.0.1.
ms-dos- Microsoft MS-DOS “operating system.” Emacs compiled with DJGPP for MS-DOS binds
system-typetoms-doseven when you run it on MS-Windows.usg-unix-v- AT&T Unix System V.
windows-nt- Microsoft Windows NT and later. The same executable supports Windows 9X, but the value of
system-typeiswindows-ntin either case.We do not wish to add new symbols to make finer distinctions unless it is absolutely necessary! In fact, we hope to eliminate some of these alternatives in the future. We recommend using
system-configurationto distinguish between different operating systems.
This function returns the name of the machine you are running on.
(system-name) ⇒ "www.gnu.org"
The symbol system-name is a variable as well as a function. In
fact, the function returns whatever value the variable
system-name currently holds. Thus, you can set the variable
system-name in case Emacs is confused about the name of your
system. The variable is also useful for constructing frame titles
(see Frame Titles).
If this variable is non-
nil, it is used instead ofsystem-namefor purposes of generating email addresses. For example, it is used when constructing the default value ofuser-mail-address. See User Identification. (Since this is done when Emacs starts up, the value actually used is the one saved when Emacs was dumped. See Building Emacs.)
This function returns the value of the environment variable var, as a string. var should be a string. If var is undefined in the environment,
getenvreturnsnil. If returns ‘""’ if var is set but null. Within Emacs, the environment variable values are kept in the Lisp variableprocess-environment.(getenv "USER") ⇒ "lewis" lewis@slug[10] % printenv PATH=.:/user/lewis/bin:/usr/bin:/usr/local/bin USER=lewis TERM=ibmapa16 SHELL=/bin/csh HOME=/user/lewis
This command sets the value of the environment variable named variable to value. variable should be a string. Internally, Emacs Lisp can handle any string. However, normally variable should be a valid shell identifier, that is, a sequence of letters, digits and underscores, starting with a letter or underscore. Otherwise, errors may occur if subprocesses of Emacs try to access the value of variable. If value is omitted or
nil,setenvremoves variable from the environment. Otherwise, value should be a string.
setenvworks by modifyingprocess-environment; binding that variable withletis also reasonable practice.
setenvreturns the new value of variable, ornilif it removed variable from the environment.
This variable is a list of strings, each describing one environment variable. The functions
getenvandsetenvwork by means of this variable.process-environment ⇒ ("l=/usr/stanford/lib/gnuemacs/lisp" "PATH=.:/user/lewis/bin:/usr/class:/nfsusr/local/bin" "USER=lewis" "TERM=ibmapa16" "SHELL=/bin/csh" "HOME=/user/lewis")If
process-environmentcontains “duplicate” elements that specify the same environment variable, the first of these elements specifies the variable, and the other “duplicates” are ignored.
This variable holds the list of environment variables Emacs inherited from its parent process. It is computed during startup, see Startup Summary.
This variable holds a string which says which character separates directories in a search path (as found in an environment variable). Its value is
":"for Unix and GNU systems, and";"for MS-DOS and MS-Windows.
This function takes a search path string such as would be the value of the
PATHenvironment variable, and splits it at the separators, returning a list of directory names.nilin this list stands for “use the current directory.” Although the function's name says “colon,” it actually uses the value ofpath-separator.(parse-colon-path ":/foo:/bar") ⇒ (nil "/foo/" "/bar/")
This variable holds the program name under which Emacs was invoked. The value is a string, and does not include a directory name.
This variable holds the directory from which the Emacs executable was invoked, or perhaps
nilif that directory cannot be determined.
If non-
nil, this is a directory within which to look for the lib-src and etc subdirectories. This is non-nilwhen Emacs can't find those directories in their standard installed locations, but can find them in a directory related somehow to the one containing the Emacs executable.
This function returns the current 1-minute, 5-minute, and 15-minute load averages, in a list.
By default, the values are integers that are 100 times the system load averages, which indicate the average number of processes trying to run. If use-float is non-
nil, then they are returned as floating point numbers and without multiplying by 100.If it is impossible to obtain the load average, this function signals an error. On some platforms, access to load averages requires installing Emacs as setuid or setgid so that it can read kernel information, and that usually isn't advisable.
If the 1-minute load average is available, but the 5- or 15-minute averages are not, this function returns a shortened list containing the available averages.
(load-average) ⇒ (169 48 36) (load-average t) ⇒ (1.69 0.48 0.36) lewis@rocky[5] % uptime 11:55am up 1 day, 19:37, 3 users, load average: 1.69, 0.48, 0.36
This variable holds the erase character that was selected in the system's terminal driver, before Emacs was started. The value is
nilif Emacs is running under a window system.
This variable says which user's init files should be used by Emacs—or
nilif none.""stands for the user who originally logged in. The value reflects command-line options such as ‘-q’ or ‘-u user’.Lisp packages that load files of customizations, or any other sort of user profile, should obey this variable in deciding where to find it. They should load the profile of the user name found in this variable. If
init-file-userisnil, meaning that the ‘-q’ option was used, then Lisp packages should not load any customization files or user profile.
This holds the nominal email address of the user who is using Emacs. Emacs normally sets this variable to a default value after reading your init files, but not if you have already set it. So you can set the variable to some other value in your init file if you do not want to use the default value.
If you don't specify uid, this function returns the name under which the user is logged in. If the environment variable
LOGNAMEis set, that value is used. Otherwise, if the environment variableUSERis set, that value is used. Otherwise, the value is based on the effective UID, not the real UID.If you specify uid, the value is the user name that corresponds to uid (which should be an integer), or
nilif there is no such user.(user-login-name) ⇒ "lewis"
This function returns the user name corresponding to Emacs's real UID. This ignores the effective UID and ignores the environment variables
LOGNAMEandUSER.
This function returns the full name of the logged-in user—or the value of the environment variable
NAME, if that is set.(user-full-name) ⇒ "Bil Lewis"If the Emacs job's user-id does not correspond to any known user (and provided
NAMEis not set), the value is"unknown".If uid is non-
nil, then it should be a number (a user-id) or a string (a login name). Thenuser-full-namereturns the full name corresponding to that user-id or login name. If you specify a user-id or login name that isn't defined, it returnsnil.
The symbols user-login-name, user-real-login-name and
user-full-name are variables as well as functions. The functions
return the same values that the variables hold. These variables allow
you to “fake out” Emacs by telling the functions what to return. The
variables are also useful for constructing frame titles (see Frame Titles).
This function returns the real UID of the user. The value may be a floating point number.
(user-real-uid) ⇒ 19
This function returns the effective UID of the user. The value may be a floating point number.
This section explains how to determine the current time and the time zone.
This function returns the current time and date as a human-readable string. The format of the string is unvarying; the number of characters used for each part is always the same, so you can reliably use
substringto extract pieces of it. It is wise to count the characters from the beginning of the string rather than from the end, as additional information may some day be added at the end.The argument time-value, if given, specifies a time to format instead of the current time. This argument should have the same form as the times obtained from
current-time(see below) and fromfile-attributes(see Definition of file-attributes). It should be a list whose first two elements are integers; a third (microsecond) element, if present, is ignored. time-value can also be a cons of two integers, but this usage is obsolete.(current-time-string) ⇒ "Wed Oct 14 22:21:05 1987"
This function returns the system's time value as a list of three integers:
(high low microsec). The integers high and low combine to give the number of seconds since 0:00 January 1, 1970 UTC (Coordinated Universal Time), which is high * 2**16 + low.The third element, microsec, gives the microseconds since the start of the current second (or 0 for systems that return time with the resolution of only one second).
The first two elements can be compared with file time values such as you get with the function
file-attributes. See Definition of file-attributes.
This function returns a list describing the time zone that the user is in.
The value has the form
(offset name). Here offset is an integer giving the number of seconds ahead of UTC (east of Greenwich). A negative value means west of Greenwich. The second element, name, is a string giving the name of the time zone. Both elements change when daylight saving time begins or ends; if the user has specified a time zone that does not use a seasonal time adjustment, then the value is constant through time.If the operating system doesn't supply all the information necessary to compute the value, the unknown elements of the list are
nil.The argument time-value, if given, specifies a time to analyze instead of the current time. The argument should have the same form as for
current-time-string(see above). Thus, you can use times obtained fromcurrent-time(see above) and fromfile-attributes. See Definition of file-attributes.
This function specifies the local time zone according to tz. If tz is
nil, that means to use an implementation-defined default time zone. If tz ist, that means to use Universal Time. Otherwise, tz should be a string specifying a time zone rule.
This function returns the current time as a floating-point number of seconds since the epoch. The argument time-value, if given, specifies a time to convert instead of the current time. The argument should have the same form as for
current-time-string(see above). Thus, it accepts the output ofcurrent-timeandfile-attributes(see Definition of file-attributes).Warning: Since the result is floating point, it may not be exact. Do not use this function if precise time stamps are required.
These functions convert time values (lists of two or three integers)
to calendrical information and vice versa. You can get time values
from the functions current-time (see Time of Day) and
file-attributes (see Definition of file-attributes).
Many operating systems are limited to time values that contain 32 bits of information; these systems typically handle only the times from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC. However, some operating systems have larger time values, and can represent times far in the past or future.
Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number −37 represents the Gregorian year 38 B.C.
This function converts a time value into calendrical information. If you don't specify time, it decodes the current time. The return value is a list of nine elements, as follows:
(seconds minutes hour day month year dow dst zone)Here is what the elements mean:
- seconds
- The number of seconds past the minute, as an integer between 0 and 59. On some operating systems, this is 60 for leap seconds.
- minutes
- The number of minutes past the hour, as an integer between 0 and 59.
- hour
- The hour of the day, as an integer between 0 and 23.
- day
- The day of the month, as an integer between 1 and 31.
- month
- The month of the year, as an integer between 1 and 12.
- year
- The year, an integer typically greater than 1900.
- dow
- The day of week, as an integer between 0 and 6, where 0 stands for Sunday.
- dst
tif daylight saving time is effect, otherwisenil.- zone
- An integer indicating the time zone, as the number of seconds east of Greenwich.
Common Lisp Note: Common Lisp has different meanings for dow and zone.
This function is the inverse of
decode-time. It converts seven items of calendrical data into a time value. For the meanings of the arguments, see the table above underdecode-time.Year numbers less than 100 are not treated specially. If you want them to stand for years above 1900, or years above 2000, you must alter them yourself before you call
encode-time.The optional argument zone defaults to the current time zone and its daylight saving time rules. If specified, it can be either a list (as you would get from
current-time-zone), a string as in theTZenvironment variable,tfor Universal Time, or an integer (as you would get fromdecode-time). The specified zone is used without any further alteration for daylight saving time.If you pass more than seven arguments to
encode-time, the first six are used as seconds through year, the last argument is used as zone, and the arguments in between are ignored. This feature makes it possible to use the elements of a list returned bydecode-timeas the arguments toencode-time, like this:(apply 'encode-time (decode-time ...))You can perform simple date arithmetic by using out-of-range values for the seconds, minutes, hour, day, and month arguments; for example, day 0 means the day preceding the given month.
The operating system puts limits on the range of possible time values; if you try to encode a time that is out of range, an error results. For instance, years before 1970 do not work on some systems; on others, years as early as 1901 do work.
These functions convert time values (lists of two or three integers) to text in a string, and vice versa.
This function parses the time-string string and returns the corresponding time value.
This function converts time (or the current time, if time is omitted) to a string according to format-string. The argument format-string may contain ‘%’-sequences which say to substitute parts of the time. Here is a table of what the ‘%’-sequences mean:
- ‘%a’
- This stands for the abbreviated name of the day of week.
- ‘%A’
- This stands for the full name of the day of week.
- ‘%b’
- This stands for the abbreviated name of the month.
- ‘%B’
- This stands for the full name of the month.
- ‘%c’
- This is a synonym for ‘%x %X’.
- ‘%C’
- This has a locale-specific meaning. In the default locale (named C), it is equivalent to ‘%A, %B %e, %Y’.
- ‘%d’
- This stands for the day of month, zero-padded.
- ‘%D’
- This is a synonym for ‘%m/%d/%y’.
- ‘%e’
- This stands for the day of month, blank-padded.
- ‘%h’
- This is a synonym for ‘%b’.
- ‘%H’
- This stands for the hour (00-23).
- ‘%I’
- This stands for the hour (01-12).
- ‘%j’
- This stands for the day of the year (001-366).
- ‘%k’
- This stands for the hour (0-23), blank padded.
- ‘%l’
- This stands for the hour (1-12), blank padded.
- ‘%m’
- This stands for the month (01-12).
- ‘%M’
- This stands for the minute (00-59).
- ‘%n’
- This stands for a newline.
- ‘%p’
- This stands for ‘AM’ or ‘PM’, as appropriate.
- ‘%r’
- This is a synonym for ‘%I:%M:%S %p’.
- ‘%R’
- This is a synonym for ‘%H:%M’.
- ‘%S’
- This stands for the seconds (00-59).
- ‘%t’
- This stands for a tab character.
- ‘%T’
- This is a synonym for ‘%H:%M:%S’.
- ‘%U’
- This stands for the week of the year (01-52), assuming that weeks start on Sunday.
- ‘%w’
- This stands for the numeric day of week (0-6). Sunday is day 0.
- ‘%W’
- This stands for the week of the year (01-52), assuming that weeks start on Monday.
- ‘%x’
- This has a locale-specific meaning. In the default locale (named ‘C’), it is equivalent to ‘%D’.
- ‘%X’
- This has a locale-specific meaning. In the default locale (named ‘C’), it is equivalent to ‘%T’.
- ‘%y’
- This stands for the year without century (00-99).
- ‘%Y’
- This stands for the year with century.
- ‘%Z’
- This stands for the time zone abbreviation (e.g., ‘EST’).
- ‘%z’
- This stands for the time zone numerical offset (e.g., ‘-0500’).
You can also specify the field width and type of padding for any of these ‘%’-sequences. This works as in
printf: you write the field width as digits in the middle of a ‘%’-sequences. If you start the field width with ‘0’, it means to pad with zeros. If you start the field width with ‘_’, it means to pad with spaces.For example, ‘%S’ specifies the number of seconds since the minute; ‘%03S’ means to pad this with zeros to 3 positions, ‘%_3S’ to pad with spaces to 3 positions. Plain ‘%3S’ pads with zeros, because that is how ‘%S’ normally pads to two positions.
The characters ‘E’ and ‘O’ act as modifiers when used between ‘%’ and one of the letters in the table above. ‘E’ specifies using the current locale's “alternative” version of the date and time. In a Japanese locale, for example,
%Exmight yield a date format based on the Japanese Emperors' reigns. ‘E’ is allowed in ‘%Ec’, ‘%EC’, ‘%Ex’, ‘%EX’, ‘%Ey’, and ‘%EY’.‘O’ means to use the current locale's “alternative” representation of numbers, instead of the ordinary decimal digits. This is allowed with most letters, all the ones that output numbers.
If universal is non-
nil, that means to describe the time as Universal Time;nilmeans describe it using what Emacs believes is the local time zone (seecurrent-time-zone).This function uses the C library function
strftime(see Formatting Calendar Time) to do most of the work. In order to communicate with that function, it first encodes its argument using the coding system specified bylocale-coding-system(see Locales); afterstrftimereturns the resulting string,format-time-stringdecodes the string using that same coding system.
This function converts seconds, a floating point number of seconds since the epoch, to a time value and returns that. To perform the inverse conversion, use
float-time.
This function converts its argument seconds into a string of years, days, hours, etc., according to format-string. The argument format-string may contain ‘%’-sequences which control the conversion. Here is a table of what the ‘%’-sequences mean:
- ‘%y’
- ‘%Y’
- The integer number of 365-day years.
- ‘%d’
- ‘%D’
- The integer number of days.
- ‘%h’
- ‘%H’
- The integer number of hours.
- ‘%m’
- ‘%M’
- The integer number of minutes.
- ‘%s’
- ‘%S’
- The integer number of seconds.
- ‘%z’
- Non-printing control flag. When it is used, other specifiers must be given in the order of decreasing size, i.e. years before days, hours before minutes, etc. Nothing will be produced in the result string to the left of ‘%z’ until the first non-zero conversion is encountered. For example, the default format used by
emacs-uptime(see emacs-uptime)"%Y, %D, %H, %M, %z%S"means that the number of seconds will always be produced, but years, days, hours, and minutes will only be shown if they are non-zero.- ‘%%’
- Produces a literal ‘%’.
Upper-case format sequences produce the units in addition to the numbers, lower-case formats produce only the numbers.
You can also specify the field width by following the ‘%’ with a number; shorter numbers will be padded with blanks. An optional period before the width requests zero-padding instead. For example,
"%.3Y"might produce"004 years".Warning: This function works only with values of seconds that don't exceed
most-positive-fixnum(see most-positive-fixnum).
Emacs provides several functions and primitives that return time, both elapsed and processor time, used by the Emacs process.
This function returns a string representing the Emacs uptime—the elapsed wall-clock time this instance of Emacs is running. The string is formatted by
format-secondsaccording to the optional argument format. For the available format descriptors, see format-seconds. If format isnilor omitted, it defaults to"%Y, %D, %H, %M, %z%S".When called interactively, it prints the uptime in the echo area.
This function returns the processor run time used by Emacs as a list of three integers:
(high low microsec). The integers high and low combine to give the number of seconds, which is high * 2**16 + low.The third element, microsec, gives the microseconds (or 0 for systems that return time with the resolution of only one second).
Note that the time returned by this function excludes the time Emacs was not using the processor, and if the Emacs process has several threads, the returned value is the sum of the processor times used up by all Emacs threads.
If the system doesn't provide a way to determine the processor run time,
get-internal-run-timereturns the same time ascurrent-time.
This function returns the duration of the Emacs initialization (see Startup Summary) in seconds, as a string. When called interactively, it prints the duration in the echo area.
These functions perform calendrical computations using time values
(the kind of list that current-time returns).
This returns the time difference t1 − t2 between two time values, in the same format as a time value.
This returns the sum of two time values, one of which ought to represent a time difference rather than a point in time. Here is how to add a number of seconds to a time value:
(time-add time (seconds-to-time seconds))
This function returns the number of days between the beginning of year 1 and time.
This returns the day number within the year corresponding to time.
You can set up a timer to call a function at a specified future time or after a certain length of idleness.
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
sit-for or read-event which can wait. Therefore, a
timer's execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
Emacs binds inhibit-quit to t before calling the timer
function, because quitting out of many timer functions can leave
things in an inconsistent state. This is normally unproblematical
because most timer functions don't do a lot of work. Indeed, for a
timer to call a function that takes substantial time to run is likely
to be annoying. If a timer function needs to allow quitting, it
should use with-local-quit (see Quitting). For example, if
a timer function calls accept-process-output to receive output
from an external process, that call should be wrapped inside
with-local-quit, to ensure that C-g works if the external
process hangs.
It is usually a bad idea for timer functions to alter buffer
contents. When they do, they usually should call undo-boundary
both before and after changing the buffer, to separate the timer's
changes from user commands' changes and prevent a single undo entry
from growing to be quite large.
Timer functions should also avoid calling functions that cause Emacs
to wait, such as sit-for (see Waiting). This can lead to
unpredictable effects, since other timers (or even the same timer) can
run while waiting. If a timer function needs to perform an action
after a certain time has elapsed, it can do this by scheduling a new
timer.
If a timer function calls functions that can change the match data, it should save and restore the match data. See Saving Match Data.
This sets up a timer that calls the function function with arguments args at time time. If repeat is a number (integer or floating point), the timer is scheduled to run again every repeat seconds after time. If repeat is
nil, the timer runs only once.time may specify an absolute or a relative time.
Absolute times may be specified using a string with a limited variety of formats, and are taken to be times today, even if already in the past. The recognized forms are ‘xxxx’, ‘x:xx’, or ‘xx:xx’ (military time), and ‘xxam’, ‘xxAM’, ‘xxpm’, ‘xxPM’, ‘xx:xxam’, ‘xx:xxAM’, ‘xx:xxpm’, or ‘xx:xxPM’. A period can be used instead of a colon to separate the hour and minute parts.
To specify a relative time as a string, use numbers followed by units. For example:
- ‘1 min’
- denotes 1 minute from now.
- ‘1 min 5 sec’
- denotes 65 seconds from now.
- ‘1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year’
- denotes exactly 103 months, 123 days, and 10862 seconds from now.
For relative time values, Emacs considers a month to be exactly thirty days, and a year to be exactly 365.25 days.
Not all convenient formats are strings. If time is a number (integer or floating point), that specifies a relative time measured in seconds. The result of
encode-timecan also be used to specify an absolute value for time.In most cases, repeat has no effect on when first call takes place—time alone specifies that. There is one exception: if time is
t, then the timer runs whenever the time is a multiple of repeat seconds after the epoch. This is useful for functions likedisplay-time.The function
run-at-timereturns a timer value that identifies the particular scheduled future action. You can use this value to callcancel-timer(see below).
A repeating timer nominally ought to run every repeat seconds, but remember that any invocation of a timer can be late. Lateness of one repetition has no effect on the scheduled time of the next repetition. For instance, if Emacs is busy computing for long enough to cover three scheduled repetitions of the timer, and then starts to wait, it will immediately call the timer function three times in immediate succession (presuming no other timers trigger before or between them). If you want a timer to run again no less than n seconds after the last invocation, don't use the repeat argument. Instead, the timer function should explicitly reschedule the timer.
This variable's value specifies the maximum number of times to repeat calling a timer function in a row, when many previously scheduled calls were unavoidably delayed.
Execute body, but give up after seconds seconds. If body finishes before the time is up,
with-timeoutreturns the value of the last form in body. If, however, the execution of body is cut short by the timeout, thenwith-timeoutexecutes all the timeout-forms and returns the value of the last of them.This macro works by setting a timer to run after seconds seconds. If body finishes before that time, it cancels the timer. If the timer actually runs, it terminates execution of body, then executes timeout-forms.
Since timers can run within a Lisp program only when the program calls a primitive that can wait,
with-timeoutcannot stop executing body while it is in the midst of a computation—only when it calls one of those primitives. So usewith-timeoutonly with a body that waits for input, not one that does a long computation.
The function y-or-n-p-with-timeout provides a simple way to use
a timer to avoid waiting too long for an answer. See Yes-or-No Queries.
This cancels the requested action for timer, which should be a timer—usually, one previously returned by
run-at-timeorrun-with-idle-timer. This cancels the effect of that call to one of these functions; the arrival of the specified time will not cause anything special to happen.
Here is how to set up a timer that runs when Emacs is idle for a certain length of time. Aside from how to set them up, idle timers work just like ordinary timers.
Set up a timer which runs when Emacs has been idle for secs seconds. The value of secs may be an integer or a floating point number; a value of the type returned by
current-idle-timeis also allowed.If repeat is
nil, the timer runs just once, the first time Emacs remains idle for a long enough time. More often repeat is non-nil, which means to run the timer each time Emacs remains idle for secs seconds.The function
run-with-idle-timerreturns a timer value which you can use in callingcancel-timer(see Timers).
Emacs becomes “idle” when it starts waiting for user input, and it
remains idle until the user provides some input. If a timer is set for
five seconds of idleness, it runs approximately five seconds after Emacs
first becomes idle. Even if repeat is non-nil, this timer
will not run again as long as Emacs remains idle, because the duration
of idleness will continue to increase and will not go down to five
seconds again.
Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness do not interfere with idle timers, because they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, and even if there have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one.
If Emacs is idle, this function returns the length of time Emacs has been idle, as a list of three integers:
(high low microsec). The integers high and low combine to give the number of seconds of idleness, which is high * 2**16 + low.The third element, microsec, gives the microseconds since the start of the current second (or 0 for systems that return time with the resolution of only one second).
When Emacs is not idle,
current-idle-timereturnsnil. This is a convenient way to test whether Emacs is idle.The main use of this function is when an idle timer function wants to “take a break” for a while. It can set up another idle timer to call the same function again, after a few seconds more idleness. Here's an example:
(defvar resume-timer nil "Timer that `timer-function' used to reschedule itself, or nil.") (defun timer-function () ;; If the user types a command whileresume-timer;; is active, the next time this function is called from ;; its main idle timer, deactivateresume-timer. (when resume-timer (cancel-timer resume-timer)) ...do the work for a while... (when taking-a-break (setq resume-timer (run-with-idle-timer ;; Compute an idle time break-length ;; more than the current value. (time-add (current-idle-time) (seconds-to-time break-length)) nil 'timer-function))))
Some idle timer functions in user Lisp packages have a loop that
does a certain amount of processing each time around, and exits when
(input-pending-p) is non-nil. That approach seems very
natural but has two problems:
To avoid these problems, don't use that technique. Instead, write
such idle timers to reschedule themselves after a brief pause, using
the method in the timer-function example above.
This section describes functions and variables for recording or manipulating terminal input. See Display, for related functions.
This function sets the mode for reading keyboard input. If interrupt is non-null, then Emacs uses input interrupts. If it is
nil, then it uses cbreak mode. The default setting is system-dependent. Some systems always use cbreak mode regardless of what is specified.When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate.
If flow is non-
nil, then Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This has no effect except in cbreak mode.The argument meta controls support for input character codes above 127. If meta is
t, Emacs converts characters with the 8th bit set into Meta characters. If meta isnil, Emacs disregards the 8th bit; this is necessary when the terminal uses it as a parity bit. If meta is neithertnornil, Emacs uses all 8 bits of input unchanged. This is good for terminals that use 8-bit character sets.If quit-char is non-
nil, it specifies the character to use for quitting. Normally this character is C-g. See Quitting.
The current-input-mode function returns the input mode settings
Emacs is currently using.
This function returns the current mode for reading keyboard input. It returns a list, corresponding to the arguments of
set-input-mode, of the form(interrupt flow meta quit)in which:
- interrupt
- is non-
nilwhen Emacs is using interrupt-driven input. Ifnil, Emacs is using cbreak mode.- flow
- is non-
nilif Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This value is meaningful only when interrupt isnil.- meta
- is
tif Emacs treats the eighth bit of input characters as the meta bit;nilmeans Emacs clears the eighth bit of every input character; any other value means Emacs uses all eight bits as the basic character code.- quit
- is the character Emacs currently uses for quitting, usually C-g.
This function returns a vector containing the last 300 input events from the keyboard or mouse. All input events are included, whether or not they were used as parts of key sequences. Thus, you always get the last 100 input events, not counting events generated by keyboard macros. (These are excluded because they are less interesting for debugging; it should be enough to see the events that invoked the macros.)
A call to
clear-this-command-keys(see Command Loop Info) causes this function to return an empty vector immediately afterward.
This function opens a dribble file named filename. When a dribble file is open, each input event from the keyboard or mouse (but not those from keyboard macros) is written in that file. A non-character event is expressed using its printed representation surrounded by ‘<...>’.
You close the dribble file by calling this function with an argument of
nil.This function is normally used to record the input necessary to trigger an Emacs bug, for the sake of a bug report.
(open-dribble-file "~/dribble") ⇒ nil
See also the open-termscript function (see Terminal Output).
The terminal output functions send output to a text terminal, or keep
track of output sent to the terminal. The variable baud-rate
tells you what Emacs thinks is the output speed of the terminal.
This variable's value is the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations such as padding.
It also affects decisions about whether to scroll part of the screen or repaint on text terminals. See Forcing Redisplay, for the corresponding functionality on graphical terminals.
The value is measured in baud.
If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal. Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not. If Emacs has the wrong value, it makes decisions that are less
than optimal. To fix the problem, set baud-rate.
This function sends string to terminal without alteration. Control characters in string have terminal-dependent effects. This function operates only on text terminals. terminal may be a terminal object, a frame, or
nilfor the selected frame's terminal. In batch mode, string is sent tostdoutwhen terminal isnil.One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how (on certain terminals) to define function key 4 to move forward four characters (by transmitting the characters C-u C-f to the computer):
(send-string-to-terminal "\eF4\^U\^F") ⇒ nil
This function is used to open a termscript file that will record all the characters sent by Emacs to the terminal. It returns
nil. Termscript files are useful for investigating problems where Emacs garbles the screen, problems that are due to incorrect Termcap entries or to undesirable settings of terminal options more often than to actual Emacs bugs. Once you are certain which characters were actually output, you can determine reliably whether they correspond to the Termcap specifications in use.You close the termscript file by calling this function with an argument of
nil.See also
open-dribble-filein Recording Input.(open-termscript "../junk/termscript") ⇒ nil
To play sound using Emacs, use the function play-sound. Only
certain systems are supported; if you call play-sound on a system
which cannot really do the job, it gives an error. Emacs version 20 and
earlier did not support sound at all.
The sound must be stored as a file in RIFF-WAVE format (‘.wav’) or Sun Audio format (‘.au’).
This function plays a specified sound. The argument, sound, has the form
(soundproperties...), where the properties consist of alternating keywords (particular symbols recognized specially) and values corresponding to them.Here is a table of the keywords that are currently meaningful in sound, and their meanings:
:filefile- This specifies the file containing the sound to play. If the file name is not absolute, it is expanded against the directory
data-directory.:datadata- This specifies the sound to play without need to refer to a file. The value, data, should be a string containing the same bytes as a sound file. We recommend using a unibyte string.
:volumevolume- This specifies how loud to play the sound. It should be a number in the range of 0 to 1. The default is to use whatever volume has been specified before.
:devicedevice- This specifies the system device on which to play the sound, as a string. The default device is system-dependent.
Before actually playing the sound,
play-soundcalls the functions in the listplay-sound-functions. Each function is called with one argument, sound.
This function is an alternative interface to playing a sound file specifying an optional volume and device.
A list of functions to be called before playing a sound. Each function is called with one argument, a property list that describes the sound.
To define system-specific X11 keysyms, set the variable
system-key-alist.
This variable's value should be an alist with one element for each system-specific keysym. Each element has the form
(code.symbol), where code is the numeric keysym code (not including the “vendor specific” bit, -2**28), and symbol is the name for the function key.For example
(168 . mute-acute)defines a system-specific key (used by HP X servers) whose numeric code is -2**28 + 168.It is not crucial to exclude from the alist the keysyms of other X servers; those do no harm, as long as they don't conflict with the ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be buffer-local. See Multiple Terminals.
You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
The name of the keysym that should stand for the Alt modifier (respectively, for Meta, Hyper, and Super). For example, here is how to swap the Meta and Alt modifiers within Emacs:
(setq x-alt-keysym 'meta) (setq x-meta-keysym 'alt)
The command-line option ‘-batch’ causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with ‘-l file’, which loads the library named file, or ‘-f function’, which calls function with no arguments, or ‘--eval form’.
Any Lisp program output that would normally go to the echo area,
either using message, or using prin1, etc., with t
as the stream, goes instead to Emacs's standard error descriptor when
in batch mode. Similarly, input that would normally come from the
minibuffer is read from the standard input descriptor.
Thus, Emacs behaves much like a noninteractive
application program. (The echo area output that Emacs itself normally
generates, such as command echoing, is suppressed entirely.)
Emacs supports the X Session Management Protocol, which is used to suspend and restart applications. In the X Window System, a program called the session manager is responsible for keeping track of the applications that are running. When the X server shuts down, the session manager asks applications to save their state, and delays the actual shutdown until they respond. An application can also cancel the shutdown.
When the session manager restarts a suspended session, it directs these applications to individually reload their saved state. It does this by specifying a special command-line argument that says what saved session to restore. For Emacs, this argument is ‘--smid session’.
Emacs supports saving state via a hook called
emacs-save-session-functions. Emacs runs this hook when the session manager tells it that the window system is shutting down. The functions are called with no arguments, and with the current buffer set to a temporary buffer. Each function can useinsertto add Lisp code to this buffer. At the end, Emacs saves the buffer in a file, called the session file.Subsequently, when the session manager restarts Emacs, it loads the session file automatically (see Loading). This is performed by a function named
emacs-session-restore, which is called during startup. See Startup Summary.If a function in
emacs-save-session-functionsreturns non-nil, Emacs tells the session manager to cancel the shutdown.
Here is an example that just inserts some text into ‘*scratch*’ when Emacs is restarted by the session manager.
(add-hook 'emacs-save-session-functions 'save-yourself-test)
(defun save-yourself-test ()
(insert "(save-current-buffer
(switch-to-buffer \"*scratch*\")
(insert \"I am restored\"))")
nil)
For those users who live backwards in time, here is information about downgrading to Emacs version 22.3. We hope you will enjoy the greater simplicity that results from the absence of many Emacs 23.3 features.
emacs-mule,
each character belongs to one and only one script. Emacs makes no
attempt to distinguish between “similar” characters occurring in
different scripts.
^ interactive spec code, the function
handle-shift-selection, and the variable
this-command-keys-shift-translated have all been removed.
Shift-translated keys are no longer treated specially, making Emacs'
handling of keybindings much more consistent.
transient-mark-mode values of the form (only
. oldvar). We instead use a more complicated scheme:
setting transient-mark-mode to only enables Transient
Mark mode for the following command only, during which the value of
transient-mark-mode is set to identity; if it is still
identity at the end of the command, Transient Mark mode is
disabled.
read-file-name and
minibuffer-complete, have been rewritten in C for greater
speed. The completion code has been considerably simplified; the
completion style can no longer be changed via
completion-styles-alist, and completing-read no longer
recognizes the special values confirm-only and
confirm-after-completion for its require-match argument.
permanent-local-hook function property has no special
meaning.
functionp function now returns t for special forms.
interactive-form symbol property has no special meaning.
Once you supply a function with an interactive form, the only way to
change it is to redefine the function.
ignore-errors macro has been moved into the cl
package.
fontp,
font-spec, and list-fonts, have all been deleted.
FontBackend X resource and the
font-backend frame parameter. On the X Window System, fonts
are always drawn using the X core font driver.
window-system variable is no longer
frame-local, and the window-system function has been removed.
list-system-processes and
process-attributes have been removed. To get information about
system processes, call an external program, such as ps.
locate-user-emacs-file and the variable
user-emacs-directory have been removed. Instead, use
hard-coded values pointing to ~/.emacs.d.
vertical-motion can no longer be told to move to a specific
column; it always puts point on the first column of a line.
display-buffer function has been rewritten in C. Its
window-splitting heuristics are a little less sophisticated, and a
little less documented. Window-splitting is handled internally,
instead of using split-window-preferred-function (which has
been removed). Windows are never split horizontally; the variable
split-width-threshold has been removed.
mode-name variable now accepts only string values, and
cannot take the form of a mode-line construct.
map-char-table has changed. It calls the
mapping function for every single character in the table, instead of
using cons cells to represent contiguous character code ranges.
input-decode-map,
local-function-key-map, search-map,
multi-query-replace-map, and
minibuffer-local-shell-command-map.
buffer-swap-text,
emacs-init-time, emacs-uptime, use-region-p,
region-active-p, start-file-process,
process-lines, image-refresh,
match-substitute-replacement, word-search-forward-lax,
and word-search-backward-lax.
read-circle,
after-init-time and before-init-time,
generate-autoload-cookie, file-local-variables-alist,
replace-search-function and replace-re-search-function,
inhibit-changing-match-data, wrap-prefix, and
line-prefix,
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If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not apply if neither you nor any third party retains the ability to install modified object code on the User Product (for example, the work has been installed in ROM).
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Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying.
“Additional permissions” are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were included in this License, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions.
When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission.
Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms:
All other non-permissive additional terms are considered “further restrictions” within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying.
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Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way.
You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).
However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.
You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.
Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License.
An “entity transaction” is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts.
You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.
A “contributor” is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's “contributor version”.
A contributor's “essential patent claims” are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, “control” includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.
Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.
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If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. “Knowingly relying” means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.
A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.
If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.
Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.
The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does.
Copyright (C) year name of author
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
program Copyright (C) year name of author
This program comes with ABSOLUTELY NO WARRANTY; for details type ‘show w’.
This is free software, and you are welcome to redistribute it
under certain conditions; type ‘show c’ for details.
The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an “about box”.
You should also get your employer (if you work as a programmer) or school, if any, to sign a “copyright disclaimer” for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see http://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read http://www.gnu.org/philosophy/why-not-lgpl.html.
This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters, and describes conventions Emacs Lisp programmers should follow.
You can automatically check some of the conventions described below by running the command M-x checkdoc RET when visiting a Lisp file. It cannot check all of the conventions, and not all the warnings it gives necessarily correspond to problems, but it is worth examining them all.
Here are conventions that you should follow when writing Emacs Lisp code intended for widespread use:
This convention is mandatory for any file that includes custom definitions. If fixing such a file to follow this convention requires an incompatible change, go ahead and make the incompatible change; don't postpone it.
Occasionally, for a command name intended for users to use, it is more convenient if some words come before the package's name prefix. And constructs that define functions, variables, etc., work better if they start with ‘defun’ or ‘defvar’, so put the name prefix later on in the name.
This recommendation applies even to names for traditional Lisp
primitives that are not primitives in Emacs Lisp—such as
copy-list. Believe it or not, there is more than one plausible
way to define copy-list. Play it safe; append your name prefix
to produce a name like foo-copy-list or mylib-copy-list
instead.
If you write a function that you think ought to be added to Emacs under
a certain name, such as twiddle-files, don't call it by that name
in your program. Call it mylib-twiddle-files in your program,
and send mail to ‘bug-gnu-emacs@gnu.org’ suggesting we add
it to Emacs. If and when we do, we can change the name easily enough.
If one prefix is insufficient, your package can use two or three alternative common prefixes, so long as they make sense.
provide at the end of each separate Lisp file.
See Named Features.
require to make sure they are loaded.
See Named Features.
(eval-when-compile (require 'bar))
This tells Emacs to load bar just before byte-compiling
foo, so that the macro definition is available during
compilation. Using eval-when-compile avoids loading bar
when the compiled version of foo is used. It should be
called before the first use of the macro in the file. See Compiling Macros.
cl package of Common Lisp extensions at
run time. Use of this package is optional, and it is not part of the
standard Emacs namespace. If your package loads cl at run time,
that could cause name clashes for users who don't use that package.
However, there is no problem with using the cl package at
compile time, with (eval-when-compile (require 'cl)). That's
sufficient for using the macros in the cl package, because the
compiler expands them before generating the byte-code.
framep and frame-live-p.
-unload-hook, where feature is the name of
the feature the package provides, and make it undo any such changes.
Using unload-feature to unload the file will run this function.
See Unloading.
(defalias 'gnus-point-at-bol
(if (fboundp 'point-at-bol)
'point-at-bol
'line-beginning-position))
eval-after-load in libraries and packages
(see Hooks for Loading). This feature is meant for personal
customizations; using it in a Lisp program is unclean, because it
modifies the behavior of another Lisp file in a way that's not visible
in that file. This is an obstacle for debugging, much like advising a
function in the other package.
utf-8-emacs (see Coding System Basics), and specify that coding in the ‘-*-’ line or the
local variables list. See Local Variables in Files.
;; XXX.el -*- coding: utf-8-emacs; -*-
indent-sexp) using the
default indentation parameters.
;; Copyright (C) year name
;; This program is free software: you can redistribute it and/or
;; modify it under the terms of the GNU General Public License as
;; published by the Free Software Foundation, either version 3 of
;; the License, or (at your option) any later version.
;; This program is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
;; GNU General Public License for more details.
;; You should have received a copy of the GNU General Public License
;; along with this program. If not, see <http://www.gnu.org/licenses/>.
If you have signed papers to assign the copyright to the Foundation, then use ‘Free Software Foundation, Inc.’ as name. Otherwise, use your name. See Library Headers.
follow-link
condition, so that the link obeys mouse-1-click-follows-link.
See Clickable Text. See Buttons, for an easy method of
implementing such clickable links.
Changing all the Emacs major modes to respect this convention was a lot of work; abandoning this convention would make that work go to waste, and inconvenience users. Please comply with it.
The reason for this rule is that a non-prefix binding for <ESC> in any context prevents recognition of escape sequences as function keys in that context.
For a state which accepts ordinary Emacs commands, or more generally any kind of state in which <ESC> followed by a function key or arrow key is potentially meaningful, then you must not define <ESC> <ESC>, since that would preclude recognizing an escape sequence after <ESC>. In these states, you should define <ESC> <ESC> <ESC> as the way to escape. Otherwise, define <ESC> <ESC> instead.
Following these conventions will make your program fit better into Emacs when it runs.
next-line or previous-line in programs; nearly
always, forward-line is more convenient as well as more
predictable and robust. See Text Lines.
In particular, don't use any of these functions:
beginning-of-buffer, end-of-buffer
replace-string, replace-regexp
insert-file, insert-buffer
If you just want to move point, or replace a certain string, or insert a file or buffer's contents, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code.
Vectors are advantageous for tables that are substantial in size and are accessed in random order (not searched front to back), provided there is no need to insert or delete elements (only lists allow that).
message function, not princ. See The Echo Area.
error
(or signal). The function error does not return.
See Signaling Errors.
Don't use message, throw, sleep-for, or
beep to report errors.
y-or-n-p or
yes-or-no-p should start with a capital letter and end with
‘? ’.
Enter the answer (default 42):
interactive, if you use a Lisp expression to produce a list
of arguments, don't try to provide the “correct” default values for
region or position arguments. Instead, provide nil for those
arguments if they were not specified, and have the function body
compute the default value when the argument is nil. For
instance, write this:
(defun foo (pos)
(interactive
(list (if specified specified-pos)))
(unless pos (setq pos default-pos))
...)
rather than this:
(defun foo (pos)
(interactive
(list (if specified specified-pos
default-pos)))
...)
This is so that repetition of the command will recompute these defaults based on the current circumstances.
You do not need to take such precautions when you use interactive specs ‘d’, ‘m’ and ‘r’, because they make special arrangements to recompute the argument values on repetition of the command.
edit-options command does: switch to another buffer and let the
user switch back at will. See Recursive Editing.
Here are ways of improving the execution speed of byte-compiled Lisp programs.
benchmark-run and
benchmark-run-compiled in benchmark.el.
memq, member,
assq, or assoc is even faster than explicit iteration. It
can be worth rearranging a data structure so that one of these primitive
search functions can be used.
byte-compile
property. If the property is non-nil, then the function is
handled specially.
For example, the following input will show you that aref is
compiled specially (see Array Functions):
(get 'aref 'byte-compile)
⇒ byte-compile-two-args
defvar definitions for these variables, like this:
(defvar foo)
Such a definition has no effect except to tell the compiler
not to warn about uses of the variable foo in this file.
require for that package to avoid compilation warnings
for them. For instance,
(eval-when-compile
(require 'foo))
with-no-warnings around it.
Here are some tips and conventions for the writing of documentation strings. You can check many of these conventions by running the command M-x checkdoc-minor-mode.
apropos.
You can fill the text if that looks good. However, rather than blindly filling the entire documentation string, you can often make it much more readable by choosing certain line breaks with care. Use blank lines between topics if the documentation string is long.
For a function, the first line should briefly answer the question, “What does this function do?” For a variable, the first line should briefly answer the question, “What does this value mean?”
Don't limit the documentation string to one line; use as many lines as you need to explain the details of how to use the function or variable. Please use complete sentences for the rest of the text too.
eval refers to its second argument as ‘FORM’, because the
actual argument name is form:
Evaluate FORM and return its value.
Also write metasyntactic variables in capital letters, such as when you show the decomposition of a list or vector into subunits, some of which may vary. ‘KEY’ and ‘VALUE’ in the following example illustrate this practice:
The argument TABLE should be an alist whose elements
have the form (KEY . VALUE). Here, KEY is ...
foo, write “foo,” not
“Foo” (which is a different symbol).
This might appear to contradict the policy of writing function argument values, but there is no real contradiction; the argument value is not the same thing as the symbol which the function uses to hold the value.
If this puts a lower-case letter at the beginning of a sentence and that annoys you, rewrite the sentence so that the symbol is not at the start of it.
Help mode automatically creates a hyperlink when a documentation string uses a symbol name inside single quotes, if the symbol has either a function or a variable definition. You do not need to do anything special to make use of this feature. However, when a symbol has both a function definition and a variable definition, and you want to refer to just one of them, you can specify which one by writing one of the words ‘variable’, ‘option’, ‘function’, or ‘command’, immediately before the symbol name. (Case makes no difference in recognizing these indicator words.) For example, if you write
This function sets the variable `buffer-file-name'.
then the hyperlink will refer only to the variable documentation of
buffer-file-name, and not to its function documentation.
If a symbol has a function definition and/or a variable definition, but those are irrelevant to the use of the symbol that you are documenting, you can write the words ‘symbol’ or ‘program’ before the symbol name to prevent making any hyperlink. For example,
If the argument KIND-OF-RESULT is the symbol `list',
this function returns a list of all the objects
that satisfy the criterion.
does not make a hyperlink to the documentation, irrelevant here, of the
function list.
Normally, no hyperlink is made for a variable without variable documentation. You can force a hyperlink for such variables by preceding them with one of the words ‘variable’ or ‘option’.
Hyperlinks for faces are only made if the face name is preceded or followed by the word ‘face’. In that case, only the face documentation will be shown, even if the symbol is also defined as a variable or as a function.
To make a hyperlink to Info documentation, write the name of the Info node (or anchor) in single quotes, preceded by ‘info node’, ‘Info node’, ‘info anchor’ or ‘Info anchor’. The Info file name defaults to ‘emacs’. For example,
See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
Finally, to create a hyperlink to URLs, write the URL in single quotes, preceded by ‘URL’. For example,
The home page for the GNU project has more information (see URL
`http://www.gnu.org/').
forward-char.
(This is normally ‘C-f’, but it may be some other character if the
user has moved key bindings.) See Keys in Documentation.
It is not practical to use ‘\\[...]’ very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use ‘\\{...}’ to display the rest of the mode's keymap.
The argument FOO can be either a number
\(a buffer position) or a string (a file name).
This prevents the open-parenthesis from being treated as the start of a defun (see Defuns).
dired-find-file is:
In Dired, visit the file or directory named on this line.
defcustom. However, if for some reason you
use defvar instead, start the doc string with a ‘*’.
See Defining Variables.
nil values are equivalent and indicate explicitly what
nil and non-nil mean.
We recommend these conventions for where to put comments and how to indent them:
indent-for-comment)
command automatically inserts such a ‘;’ in the right place, or
aligns such a comment if it is already present.
This and following examples are taken from the Emacs sources.
(setq base-version-list ; there was a base
(assoc (substring fn 0 start-vn) ; version to which
file-version-assoc-list)) ; this looks like
; a subversion
(prog1 (setq auto-fill-function
...
...
;; update mode line
(force-mode-line-update)))
We also normally use two semicolons for comments outside functions.
;; This Lisp code is run in Emacs
;; when it is to operate as a server
;; for other processes.
Every function that has no documentation string (presumably one that is
used only internally within the package it belongs to), should instead
have a two-semicolon comment right before the function, explaining what
the function does and how to call it properly. Explain precisely what
each argument means and how the function interprets its possible values.
Another use for triple-semicolon comments is for commenting out lines within a function. We use three semicolons for this precisely so that they remain at the left margin. By default, Outline minor mode does not consider a comment to be a heading (even if it starts with at least three semicolons) if the semicolons are followed by at least two spaces. Thus, if you add an introductory comment to the commented out code, make sure to indent it by at least two spaces after the three semicolons.
(defun foo (a)
;;; This is no longer necessary.
;;; (force-mode-line-update)
(message "Finished with %s" a))
When commenting out entire functions, use two semicolons.
;;;; The kill ring
The indentation commands of the Lisp modes in Emacs, such as M-;
(indent-for-comment) and <TAB> (lisp-indent-line),
automatically indent comments according to these conventions,
depending on the number of semicolons. See Manipulating Comments.
Emacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. This section explains these conventions.
We'll start with an example, a package that is included in the Emacs distribution.
Parts of this example reflect its status as part of Emacs; for example, the copyright notice lists the Free Software Foundation as the copyright holder, and the copying permission says the file is part of Emacs. When you write a package and post it, the copyright holder would be you (unless your employer claims to own it instead), and you should get the suggested copying permission from the end of the GNU General Public License itself. Don't say your file is part of Emacs if we haven't installed it in Emacs yet!
With that warning out of the way, on to the example:
;;; lisp-mnt.el --- minor mode for Emacs Lisp maintainers
;; Copyright (C) 1992 Free Software Foundation, Inc.
;; Author: Eric S. Raymond <esr@snark.thyrsus.com>
;; Maintainer: Eric S. Raymond <esr@snark.thyrsus.com>
;; Created: 14 Jul 1992
;; Version: 1.2
;; Keywords: docs
;; This file is part of GNU Emacs.
...
;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
The very first line should have this format:
;;; filename --- description
The description should be complete in one line. If the file needs a ‘-*-’ specification, put it after description.
After the copyright notice come several header comment lines, each beginning with ‘;; header-name:’. Here is a table of the conventional possibilities for header-name:
If there are multiple authors, you can list them on continuation lines
led by ;; and a tab character, like this:
;; Author: Ashwin Ram <Ram-Ashwin@cs.yale.edu>
;; Dave Sill <de5@ornl.gov>
;; Dave Brennan <brennan@hal.com>
;; Eric Raymond <esr@snark.thyrsus.com>
The idea behind the ‘Author’ and ‘Maintainer’ lines is to make possible a Lisp function to “send mail to the maintainer” without having to mine the name out by hand.
Be sure to surround the network address with ‘<...>’ if
you include the person's full name as well as the network address.
finder-by-keyword help command.
Please use that command to see a list of the meaningful keywords.
This field is important; it's how people will find your package when they're looking for things by topic area. To separate the keywords, you can use spaces, commas, or both.
Just about every Lisp library ought to have the ‘Author’ and ‘Keywords’ header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names—they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the library file. These should be separated by blank lines from anything else. Here is a table of them:
This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers.
This section explains the steps involved in building the Emacs executable. You don't have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs maintenance.
Compilation of the C source files in the src directory produces an executable file called temacs, also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.
The command ‘temacs -l loadup’ uses temacs to create the real runnable Emacs executable. These arguments direct temacs to evaluate the Lisp files specified in the file loadup.el. These files set up the normal Emacs editing environment, resulting in an Emacs that is still impure but no longer bare.
It takes a substantial time to load the standard Lisp files. Luckily, you don't have to do this each time you run Emacs; temacs can dump out an executable program called emacs that has these files preloaded. emacs starts more quickly because it does not need to load the files. This is the Emacs executable that is normally installed.
To create emacs, use the command ‘temacs -batch -l loadup
dump’. The purpose of ‘-batch’ here is to prevent temacs
from trying to initialize any of its data on the terminal; this ensures
that the tables of terminal information are empty in the dumped Emacs.
The argument ‘dump’ tells loadup.el to dump a new executable
named emacs. The variable preloaded-file-list stores a
list of the Lisp files that were dumped with the emacs executable.
Some operating systems don't support dumping. On those systems, you must start Emacs with the ‘temacs -l loadup’ command each time you use it. This takes a substantial time, but since you need to start Emacs once a day at most—or once a week if you never log out—the extra time is not too severe a problem.
You can specify additional files to preload by writing a library named site-load.el that loads them. You may need to add a definition
#define SITELOAD_PURESIZE_EXTRA n
to make n added bytes of pure space to hold the additional files. (Try adding increments of 20000 until it is big enough.) However, the advantage of preloading additional files decreases as machines get faster. On modern machines, it is usually not advisable.
After loadup.el reads site-load.el, it finds the
documentation strings for primitive and preloaded functions (and
variables) in the file etc/DOC where they are stored, by
calling Snarf-documentation (see Accessing Documentation).
You can specify other Lisp expressions to execute just before dumping by putting them in a library named site-init.el. This file is executed after the documentation strings are found.
If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs:
nil value for
byte-compile-dynamic-docstrings as a local variable in each of these
files, and load them with either site-load.el or
site-init.el. (This method has the drawback that the
documentation strings take up space in Emacs all the time.)
It is not advisable to put anything in site-load.el or site-init.el that would alter any of the features that users expect in an ordinary unmodified Emacs. If you feel you must override normal features for your site, do it with default.el, so that users can override your changes if they wish. See Startup Summary.
In a package that can be preloaded, it is sometimes useful to
specify a computation to be done when Emacs subsequently starts up.
For this, use eval-at-startup:
This evaluates the body forms, either immediately if running in an Emacs that has already started up, or later when Emacs does start up. Since the value of the body forms is not necessarily available when the
eval-at-startupform is run, that form always returnsnil.
This function dumps the current state of Emacs into an executable file to-file. It takes symbols from from-file (this is normally the executable file temacs).
If you want to use this function in an Emacs that was already dumped, you must run Emacs with ‘-batch’.
Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data created during an Emacs session are kept; see the following section for information on normal storage. Pure storage is used for certain data in the preloaded standard Lisp files—data that should never change during actual use of Emacs.
Pure storage is allocated only while temacs is loading the
standard preloaded Lisp libraries. In the file emacs, it is
marked as read-only (on operating systems that permit this), so that
the memory space can be shared by all the Emacs jobs running on the
machine at once. Pure storage is not expandable; a fixed amount is
allocated when Emacs is compiled, and if that is not sufficient for
the preloaded libraries, temacs allocates dynamic memory for
the part that didn't fit. If that happens, you should increase the
compilation parameter PURESIZE in the file
src/puresize.h and rebuild Emacs, even though the resulting
image will work: garbage collection is disabled in this situation,
causing a memory leak. Such an overflow normally won't happen unless you
try to preload additional libraries or add features to the standard
ones. Emacs will display a warning about the overflow when it
starts.
This function makes a copy in pure storage of object, and returns it. It copies a string by simply making a new string with the same characters, but without text properties, in pure storage. It recursively copies the contents of vectors and cons cells. It does not make copies of other objects such as symbols, but just returns them unchanged. It signals an error if asked to copy markers.
This function is a no-op except while Emacs is being built and dumped; it is usually called only in the file emacs/lisp/loaddefs.el, but a few packages call it just in case you decide to preload them.
The value of this variable is the number of bytes of pure storage allocated so far. Typically, in a dumped Emacs, this number is very close to the total amount of pure storage available—if it were not, we would preallocate less.
This variable determines whether
defunshould make a copy of the function definition in pure storage. If it is non-nil, then the function definition is copied into pure storage.This flag is
twhile loading all of the basic functions for building Emacs initially (allowing those functions to be sharable and non-collectible). Dumping Emacs as an executable always writesnilin this variable, regardless of the value it actually has before and after dumping.You should not change this flag in a running Emacs.
When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory in blocks of 1k bytes. Each block is used for one type of Lisp object, so symbols, cons cells, markers, etc., are segregated in distinct blocks in memory. (Vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object, while small strings are packed into blocks of 8k bytes.)
It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. (This name is traditional, but “garbage recycler” might be a more intuitive metaphor for this facility.)
The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible.
When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second (“sweep”) phase of the garbage collector arranges to reuse them.
The sweep phase puts unused cons cells onto a free list
for future allocation; likewise for symbols and markers. It compacts
the accessible strings so they occupy fewer 8k blocks; then it frees the
other 8k blocks. Vectors, buffers, windows, and other large objects are
individually allocated and freed using malloc and free.
Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues untilgc-cons-thresholdbytes have been used.This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection).
This command runs a garbage collection, and returns information on the amount of space in use. (Garbage collection can also occur spontaneously if you use more than
gc-cons-thresholdbytes of Lisp data since the previous garbage collection.)
garbage-collectreturns a list containing the following information:((used-conses . free-conses) (used-syms . free-syms) (used-miscs . free-miscs) used-string-chars used-vector-slots (used-floats . free-floats) (used-intervals . free-intervals) (used-strings . free-strings))Here is an example:
(garbage-collect) ⇒ ((106886 . 13184) (9769 . 0) (7731 . 4651) 347543 121628 (31 . 94) (1273 . 168) (25474 . 3569))Here is a table explaining each element:
- used-conses
- The number of cons cells in use.
- free-conses
- The number of cons cells for which space has been obtained from the operating system, but that are not currently being used.
- used-syms
- The number of symbols in use.
- free-syms
- The number of symbols for which space has been obtained from the operating system, but that are not currently being used.
- used-miscs
- The number of miscellaneous objects in use. These include markers and overlays, plus certain objects not visible to users.
- free-miscs
- The number of miscellaneous objects for which space has been obtained from the operating system, but that are not currently being used.
- used-string-chars
- The total size of all strings, in characters.
- used-vector-slots
- The total number of elements of existing vectors.
- used-floats
- The number of floats in use.
- free-floats
- The number of floats for which space has been obtained from the operating system, but that are not currently being used.
- used-intervals
- The number of intervals in use. Intervals are an internal data structure used for representing text properties.
- free-intervals
- The number of intervals for which space has been obtained from the operating system, but that are not currently being used.
- used-strings
- The number of strings in use.
- free-strings
- The number of string headers for which the space was obtained from the operating system, but which are currently not in use. (A string object consists of a header and the storage for the string text itself; the latter is only allocated when the string is created.)
If there was overflow in pure space (see the previous section),
garbage-collectreturnsnil, because a real garbage collection can not be done in this situation.
If this variable is non-
nil, Emacs displays a message at the beginning and end of garbage collection. The default value isnil, meaning there are no such messages.
This is a normal hook that is run at the end of garbage collection. Garbage collection is inhibited while the hook functions run, so be careful writing them.
The value of this variable is the number of bytes of storage that must be allocated for Lisp objects after one garbage collection in order to trigger another garbage collection. A cons cell counts as eight bytes, a string as one byte per character plus a few bytes of overhead, and so on; space allocated to the contents of buffers does not count. Note that the subsequent garbage collection does not happen immediately when the threshold is exhausted, but only the next time the Lisp evaluator is called.
The initial threshold value is 400,000. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program that creates lots of Lisp data.
You can make collections more frequent by specifying a smaller value, down to 10,000. A value less than 10,000 will remain in effect only until the subsequent garbage collection, at which time
garbage-collectwill set the threshold back to 10,000.
The value of this variable specifies the amount of consing before a garbage collection occurs, as a fraction of the current heap size. This criterion and
gc-cons-thresholdapply in parallel, and garbage collection occurs only when both criteria are satisfied.As the heap size increases, the time to perform a garbage collection increases. Thus, it can be desirable to do them less frequently in proportion.
The value returned by garbage-collect describes the amount of
memory used by Lisp data, broken down by data type. By contrast, the
function memory-limit provides information on the total amount of
memory Emacs is currently using.
This function returns the address of the last byte Emacs has allocated, divided by 1024. We divide the value by 1024 to make sure it fits in a Lisp integer.
You can use this to get a general idea of how your actions affect the memory usage.
This variable is
tif Emacs is close to out of memory for Lisp objects, andnilotherwise.
This returns a list of numbers that count the number of objects created in this Emacs session. Each of these counters increments for a certain kind of object. See the documentation string for details.
This variable contains the total number of garbage collections done so far in this Emacs session.
This variable contains the total number of seconds of elapsed time during garbage collection so far in this Emacs session, as a floating point number.
These functions and variables give information about the total amount
of memory allocation that Emacs has done, broken down by data type.
Note the difference between these and the values returned by
(garbage-collect); those count objects that currently exist, but
these count the number or size of all allocations, including those for
objects that have since been freed.
The total number of cons cells that have been allocated so far in this Emacs session.
The total number of floats that have been allocated so far in this Emacs session.
The total number of vector cells that have been allocated so far in this Emacs session.
The total number of symbols that have been allocated so far in this Emacs session.
The total number of string characters that have been allocated so far in this Emacs session.
The total number of miscellaneous objects that have been allocated so far in this Emacs session. These include markers and overlays, plus certain objects not visible to users.
The total number of intervals that have been allocated so far in this Emacs session.
The total number of strings that have been allocated so far in this Emacs session.
Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here.
An example of a special form is the definition of or, from
eval.c. (An ordinary function would have the same general
appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
doc: /* Eval args until one of them yields non-nil, then return that
value. The remaining args are not evalled at all.
If all args return nil, return nil.
usage: (or CONDITIONS ...) */)
(args)
Lisp_Object args;
{
register Lisp_Object val = Qnil;
struct gcpro gcpro1;
GCPRO1 (args);
while (CONSP (args))
{
val = Feval (XCAR (args));
if (!NILP (val))
break;
args = XCDR (args);
}
UNGCPRO;
return val;
}
Let's start with a precise explanation of the arguments to the
DEFUN macro. Here is a template for them:
DEFUN (lname, fname, sname, min, max, interactive, doc)
or.
For. Remember that the arguments must
be of type Lisp_Object; various macros and functions for creating
values of type Lisp_Object are declared in the file
lisp.h.
or allows a minimum of zero arguments.
UNEVALLED,
indicating a special form that receives unevaluated arguments, or
MANY, indicating an unlimited number of evaluated arguments (the
equivalent of &rest). Both UNEVALLED and MANY are
macros. If max is a number, it may not be less than min and
it may not be greater than eight.
interactive in a Lisp function. In the case of
or, it is 0 (a null pointer), indicating that or cannot be
called interactively. A value of "" indicates a function that
should receive no arguments when called interactively. If the value
begins with a ‘(’, the string is evaluated as a Lisp form.
If the last line of the documentation string begins with the keyword ‘usage:’, the rest of the line is treated as the argument list for documentation purposes. This way, you can use different argument names in the documentation string from the ones used in the C code. ‘usage:’ is required if the function has an unlimited number of arguments.
All the usual rules for documentation strings in Lisp code (see Documentation Tips) apply to C code documentation strings too.
After the call to the DEFUN macro, you must write the argument
name list that every C function must have, followed by ordinary C
declarations for the arguments. For a function with a fixed maximum
number of arguments, declare a C argument for each Lisp argument, and
give them all type Lisp_Object. When a Lisp function has no
upper limit on the number of arguments, its implementation in C actually
receives exactly two arguments: the first is the number of Lisp
arguments, and the second is the address of a block containing their
values. They have types int and Lisp_Object *.
Within the function For itself, note the use of the macros
GCPRO1 and UNGCPRO. GCPRO1 is used to
“protect” a variable from garbage collection—to inform the garbage
collector that it must look in that variable and regard its contents
as an accessible object. GC protection is necessary whenever you call
Feval or anything that can directly or indirectly call
Feval. At such a time, any Lisp object that this function may
refer to again must be protected somehow.
It suffices to ensure that at least one pointer to each object is
GC-protected; that way, the object cannot be recycled, so all pointers
to it remain valid. Thus, a particular local variable can do without
protection if it is certain that the object it points to will be
preserved by some other pointer (such as another local variable which
has a GCPRO)19. Otherwise, the local
variable needs a GCPRO.
The macro GCPRO1 protects just one local variable. If you
want to protect two variables, use GCPRO2 instead; repeating
GCPRO1 will not work. Macros GCPRO3, GCPRO4,
GCPRO5, and GCPRO6 also exist. All these macros
implicitly use local variables such as gcpro1; you must declare
these explicitly, with type struct gcpro. Thus, if you use
GCPRO2, you must declare gcpro1 and gcpro2.
Alas, we can't explain all the tricky details here.
UNGCPRO cancels the protection of the variables that are
protected in the current function. It is necessary to do this
explicitly.
Built-in functions that take a variable number of arguments actually
accept two arguments at the C level: the number of Lisp arguments, and
a Lisp_Object * pointer to a C vector containing those Lisp
arguments. This C vector may be part of a Lisp vector, but it need
not be. The responsibility for using GCPRO to protect the Lisp
arguments from GC if necessary rests with the caller in this case,
since the caller allocated or found the storage for them.
You must not use C initializers for static or global variables unless the variables are never written once Emacs is dumped. These variables with initializers are allocated in an area of memory that becomes read-only (on certain operating systems) as a result of dumping Emacs. See Pure Storage.
Do not use static variables within functions—place all static
variables at top level in the file. This is necessary because Emacs on
some operating systems defines the keyword static as a null
macro. (This definition is used because those systems put all variables
declared static in a place that becomes read-only after dumping, whether
they have initializers or not.)
Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like this:
defsubr (&subr-structure-name);
Here subr-structure-name is the name you used as the third
argument to DEFUN.
If you add a new primitive to a file that already has Lisp primitives
defined in it, find the function (near the end of the file) named
syms_of_something, and add the call to defsubr
there. If the file doesn't have this function, or if you create a new
file, add to it a syms_of_filename (e.g.,
syms_of_myfile). Then find the spot in emacs.c where all
of these functions are called, and add a call to
syms_of_filename there.
The function syms_of_filename is also the place to define
any C variables that are to be visible as Lisp variables.
DEFVAR_LISP makes a C variable of type Lisp_Object visible
in Lisp. DEFVAR_INT makes a C variable of type int
visible in Lisp with a value that is always an integer.
DEFVAR_BOOL makes a C variable of type int visible in Lisp
with a value that is either t or nil. Note that variables
defined with DEFVAR_BOOL are automatically added to the list
byte-boolean-vars used by the byte compiler.
If you define a file-scope C variable of type Lisp_Object,
you must protect it from garbage-collection by calling staticpro
in syms_of_filename, like this:
staticpro (&variable);
Here is another example function, with more complicated arguments. This comes from the code in window.c, and it demonstrates the use of macros and functions to manipulate Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2,
"xSpecify coordinate pair: \nXExpression which evals to window: ",
"Return non-nil if COORDINATES is in WINDOW.\n\
COORDINATES is a cons of the form (X . Y), X and Y being distances\n\
...
If they are on the border between WINDOW and its right sibling,\n\
`vertical-line' is returned.")
(coordinates, window)
register Lisp_Object coordinates, window;
{
int x, y;
CHECK_LIVE_WINDOW (window, 0);
CHECK_CONS (coordinates, 1);
x = XINT (Fcar (coordinates));
y = XINT (Fcdr (coordinates));
switch (coordinates_in_window (XWINDOW (window), &x, &y))
{
case 0: /* NOT in window at all. */
return Qnil;
case 1: /* In text part of window. */
return Fcons (make_number (x), make_number (y));
case 2: /* In mode line of window. */
return Qmode_line;
case 3: /* On right border of window. */
return Qvertical_line;
default:
abort ();
}
}
Note that C code cannot call functions by name unless they are defined
in C. The way to call a function written in Lisp is to use
Ffuncall, which embodies the Lisp function funcall. Since
the Lisp function funcall accepts an unlimited number of
arguments, in C it takes two: the number of Lisp-level arguments, and a
one-dimensional array containing their values. The first Lisp-level
argument is the Lisp function to call, and the rest are the arguments to
pass to it. Since Ffuncall can call the evaluator, you must
protect pointers from garbage collection around the call to
Ffuncall.
The C functions call0, call1, call2, and so on,
provide handy ways to call a Lisp function conveniently with a fixed
number of arguments. They work by calling Ffuncall.
eval.c is a very good file to look through for examples; lisp.h contains the definitions for some important macros and functions.
If you define a function which is side-effect free, update the code
in byte-opt.el which binds side-effect-free-fns and
side-effect-and-error-free-fns so that the compiler optimizer
knows about it.
GNU Emacs Lisp manipulates many different types of data. The actual data are stored in a heap and the only access that programs have to it is through pointers. Each pointer is 32 bits wide on 32-bit machines, and 64 bits wide on 64-bit machines; three of these bits are used for the tag that identifies the object's type, and the remainder are used to address the object.
Because Lisp objects are represented as tagged pointers, it is always
possible to determine the Lisp data type of any object. The C data type
Lisp_Object can hold any Lisp object of any data type. Ordinary
variables have type Lisp_Object, which means they can hold any
type of Lisp value; you can determine the actual data type only at run
time. The same is true for function arguments; if you want a function
to accept only a certain type of argument, you must check the type
explicitly using a suitable predicate (see 类型判定).
Two structures are used to represent buffers in C. The
buffer_text structure contains fields describing the text of a
buffer; the buffer structure holds other fields. In the case
of indirect buffers, two or more buffer structures reference
the same buffer_text structure.
Here are some of the fields in struct buffer_text:
beggptgpt_bytezz_bytegap_sizemodiffsave_modiffchars_modiffoverlay_modiffmodiff is incremented after each
buffer-modification event, and is never otherwise changed;
save_modiff contains the value of modiff the last time
the buffer was visited or saved; chars_modiff counts only
modifications to the characters in the buffer, ignoring all other
kinds of changes; and overlay_modiff counts only modifications
to the overlays.
beg_unchangedend_unchangedunchanged_modifiedoverlay_unchanged_modifiedmodiff and overlay_modiff, respectively,
after the last compelete redisplay. If their current values match
modiff or overlay_modiff, that means
beg_unchanged and end_unchanged contain no useful
information.
markerschain are the other
markers referring to this buffer text.
intervalsSome of the fields of struct buffer are:
nextown_textstruct buffer_text structure that ordinarily holds the buffer
contents. In indirect buffers, this field is not used.
textbuffer_text structure for this buffer. In an
ordinary buffer, this is the own_text field above. In an
indirect buffer, this is the own_text field of the base buffer.
ptpt_bytebegvbegv_bytezvzv_bytebase_bufferlocal_flagsDEFVAR_PER_BUFFER, and their buffer-local bindings are stored
in fields in the buffer structure itself. (Some of these fields are
described in this table.)
modtimeauto_save_modifiedlast_window_startwindow-start position in the buffer as of the last time the
buffer was displayed in a window.
clip_changedprevent_redisplay_optimizations_poverlay_centeroverlays_beforeoverlays_afteroverlays_before is sorted in order of decreasing end position,
and overlays_after is sorted in order of increasing beginning
position.
namesave_lengthbuffer_text structure because indirect buffers are never
saved.
directorydefault-directory (see File Name Expansion).
filenamenil. This is
the value of the buffer-local variable buffer-file-name
(see Buffer File Name).
undo_listbacked_upauto_save_file_nameread_onlyfile_formatfile_truenameinvisibility_specdisplay_countdisplay_timebuffer- and have
underscores replaced with dashes. For instance, undo_list
stores the value of buffer-undo-list. See Standard Buffer-Local Variables.
markmarkers. See The Mark.
local_var_alistmajor_modelisp-mode.
mode_name"Lisp".
keymapabbrev_tablesyntax_tablecategory_tabledisplay_tabledowncase_tableupcase_tablecase_canon_tableminor_modespt_markerbegv_markerzv_markerpt, begv, and zv respectively, for this buffer
when the buffer is not current.
mode_line_formatheader_line_formatcase_fold_searchtab_widthfill_columnleft_marginauto_fill_functiontruncate_linesword_wrapctl_arrowselective_displayselective_display_ellipsesoverwrite_modeabbrev_modedisplay_tablemark_activeenable_multibyte_charactersbuffer_file_coding_systemauto_save_file_formatcache_long_line_scanspoint_before_scrollleft_fringe_widthright_fringe_widthfringes_outside_marginsscroll_bar_widthindicate_empty_linesindicate_buffer_boundariesfringe_indicator_alistfringe_cursor_alistscroll_up_aggressivelyscroll_down_aggressivelycursor_typecursor_in_non_selected_windowsmode_line_format stores the value of mode-line-format.
See Standard Buffer-Local Variables.
last_selected_windownil
if that window no longer displays this buffer.
Windows have the following accessible fields:
framemini_pnil if this window is a minibuffer window.
parentParent windows do not display buffers, and play little role in display
except to shape their child windows. Emacs Lisp programs usually have
no access to the parent windows; they operate on the windows at the
leaves of the tree, which actually display buffers.
hchildvchildhchild is used if the window is subdivided
horizontally by child windows, and vchild if it is subdivided
vertically.
nextprevnext is
nil if the window is the rightmost or bottommost in its group;
prev is nil if it is the leftmost or topmost in its
group.
left_coltop_linetotal_colstotal_linesbufferstartpointmforce_startnil, it says that the window has been
scrolled explicitly by the Lisp program. This affects what the next
redisplay does if point is off the screen: instead of scrolling the
window to show the text around point, it moves point to a location that
is on the screen.
frozen_window_start_pstart of this window should not be changed, even if point
gets invisible.
start_at_line_begnil means current value of start was the beginning of a line
when it was chosen.
use_timeget-lru-window uses this field.
sequence_numberlast_modifiedmodiff field of the window's buffer, as of the last time
a redisplay completed in this window.
last_overlay_modifiedoverlay_modiff field of the window's buffer, as of the last
time a redisplay completed in this window.
last_pointlast_had_starnil value means the window's buffer was “modified” when the
window was last updated.
vertical_scroll_barleft_margin_widthright_margin_widthnil means to use the buffer's value of left-margin-width
or right-margin-width.
window_end_posz minus the buffer position of the last glyph
in the current matrix of the window. The value is only valid if
window_end_valid is not nil.
window_end_byteposwindow_end_pos.
window_end_vposwindow_end_pos.
window_end_validnil value if window_end_pos is truly
valid. This is nil if nontrivial redisplay is preempted since in that
case the display that window_end_pos was computed for did not get
onto the screen.
cursorlast_cursorcursor as of the last redisplay that finished.
phys_cursorphys_cursor_typephys_cursor_on_pcursor_off_plast_cursor_off_pcursor_off_p as of the time of
the last redisplay.
must_be_updated_phscrollvscrolldedicatednil if this window is dedicated to its buffer.
display_tablenil if none is specified for it.
update_mode_linenil means this window's mode line needs to be updated.
base_line_numbernil.
This is used for displaying the line number of point in the mode line.
base_line_posnil meaning none is known.
region_showingnil.
column_number_displayednil
if column numbers are not being displayed.
current_matrixdesired_matrixnamecommandnil if the
process is running or t if the process is stopped.
filternil.
sentinelnil.
bufferpidchildpnil if this is really a child process.
It is nil for a network or serial connection.
markkill_without_queryraw_status_lowraw_status_highwait system call.
statusprocess-status should return it.
tickupdate_tickpty_flagnil if communication with the subprocess uses a PTY;
nil if it uses a pipe.
infdoutfdsubttynil.)
tty_namenil if it is using pipes.
decode_coding_systemdecoding_bufdecoding_carryoverencode_coding_systemencoding_bufencoding_carryoverinherit_coding_system_flagcoding-system of the process buffer from the
coding system used to decode process output.
typereal, network,
serial
Here is the complete list of the error symbols in standard Emacs,
grouped by concept. The list includes each symbol's message (on the
error-message property of the symbol) and a cross reference to a
description of how the error can occur.
Each error symbol has an error-conditions property that is a
list of symbols. Normally this list includes the error symbol itself
and the symbol error. Occasionally it includes additional
symbols, which are intermediate classifications, narrower than
error but broader than a single error symbol. For example, all
the errors in accessing files have the condition file-error. If
we do not say here that a certain error symbol has additional error
conditions, that means it has none.
As a special exception, the error symbol quit does not have the
condition error, because quitting is not considered an error.
See Errors, for an explanation of how errors are generated and handled.
error"error"quit"Quit"args-out-of-range"Args out of range"arith-error"Arithmetic error"beginning-of-buffer"Beginning of buffer"buffer-read-only"Buffer is read-only"coding-system-error"Invalid coding system"cyclic-function-indirection"Symbol's chain of function indirections contains a loop"cyclic-variable-indirection"Symbol's chain of variable indirections contains a loop"end-of-buffer"End of buffer"end-of-file"End of file during parsing"file-error,
because it pertains to the Lisp reader, not to file I/O.file-already-existsfile-error.file-date-errorfile-error. It occurs when
copy-file tries and fails to set the last-modification time of
the output file.file-errorfile-error is present. Thus,
the error-strings are not very relevant. However, these error symbols
do have error-message properties, and if no data is provided,
the error-message property is used.file-lockedfile-error.file-supersessionfile-error.ftp-errorfile-error, which results from problems
in accessing a remote file using ftp.invalid-function"Invalid function"invalid-read-syntax"Invalid read syntax"invalid-regexp"Invalid regexp"mark-inactive"The mark is not active now"no-catch"No catch for tag"scan-error"Scan error"search-failed"Search failed"setting-constant"Attempt to set a constant symbol"nil and t,
and any symbols that start with ‘:’,
may not be changed.text-read-only"Text is read-only"buffer-read-only.undefined-color"Undefined color"void-function"Symbol's function definition is void"void-variable"Symbol's value as variable is void"wrong-number-of-arguments"Wrong number of arguments"wrong-type-argument"Wrong type argument"These kinds of error, which are classified as special cases of
arith-error, can occur on certain systems for invalid use of
mathematical functions.
domain-error"Arithmetic domain error"overflow-error"Arithmetic overflow error"domain-error.range-error"Arithmetic range error"singularity-error"Arithmetic singularity error"domain-error.underflow-error"Arithmetic underflow error"domain-error.The table below lists the general-purpose Emacs variables that automatically become buffer-local in each buffer. Most become buffer-local only when set; a few of them are always local in every buffer. Many Lisp packages define such variables for their internal use, but we don't try to list them all here.
Every buffer-specific minor mode defines a buffer-local variable named ‘modename-mode’. See Minor Mode Conventions. Minor mode variables will not be listed here.
auto-fill-functionbuffer-auto-save-file-formatbuffer-auto-save-file-namebuffer-backed-upbuffer-display-countbuffer-display-tablebuffer-display-timebuffer-file-coding-systembuffer-file-formatbuffer-file-namebuffer-file-numberbuffer-file-truenamebuffer-file-typebuffer-invisibility-specbuffer-offer-savebuffer-save-without-querybuffer-read-onlybuffer-saved-sizebuffer-undo-listcache-long-line-scanscase-fold-searchcomment-columnctl-arrowcursor-in-non-selected-windowscursor-typedefault-directorydefun-prompt-regexpdesktop-save-bufferenable-multibyte-charactersfill-columnfill-prefixfont-lock-defaultsfringe-cursor-alistfringe-indicator-alistfringes-outside-marginsgoal-columnheader-line-formatindicate-buffer-boundariesindicate-empty-linesleft-fringe-widthleft-marginleft-margin-widthline-spacinglocal-abbrev-tablemajor-modemark-activemark-ringmode-line-buffer-identificationmode-line-formatmode-line-modifiedmode-line-processmode-namepoint-before-scrollright-fringe-widthright-margin-widthsave-buffer-coding-systemscroll-bar-widthscroll-down-aggressivelyscroll-up-aggressivelyselective-displayselective-display-ellipsestab-widthtruncate-linesvertical-scroll-barwindow-size-fixedwrite-contents-functionsThe following symbols are used as the names for various keymaps. Some of these exist when Emacs is first started, others are loaded only when their respective mode is used. This is not an exhaustive list.
Several keymaps are used in the minibuffer. See Completion Commands.
Almost all of these maps are used as local maps. Indeed, of the modes that presently exist, only Vip mode and Terminal mode ever change the global keymap.
apropos-mode-mapapropos buffers.
Buffer-menu-mode-mapc-mode-mapcommand-history-mapctl-x-4-mapctl-x-5-mapctl-x-mapcustom-mode-mapdebugger-mode-mapdired-mode-mapdired-mode buffers.
edit-abbrevs-mapedit-abbrevs.
edit-tab-stops-mapedit-tab-stops.
electric-buffer-menu-mode-mapelectric-history-mapemacs-lisp-mode-mapesc-mapfacemenu-menufacemenu-background-menufacemenu-face-menufacemenu-foreground-menufacemenu-indentation-menufacemenu-justification-menufacemenu-special-menulocal-function-key-mapfundamental-mode-mapglobal-mapgrep-mode-mapgrep-mode buffers.
help-maphelp-mode-mapHelper-help-mapInfo-edit-mapInfo-mode-mapinput-decode-mapisearch-mode-mapkey-translation-maplocal-function-key-map. See Translation Keymaps.
kmacro-maplisp-interaction-mode-maplisp-mode-mapmenu-bar-edit-menumenu-bar-file-menumenu-bar-help-menumenu-bar-mule-menumenu-bar-search-menumenu-bar-tools-menumode-specific-mapdisplay-bindings),
where it describes the main use of the C-c prefix key.
multi-query-replace-mapquery-replace-map for multi-buffer
replacements. See query-replace-map.
occur-mode-mapquery-replace-mapquery-replace and related
commands; also for y-or-n-p and map-y-or-n-p. The functions
that use this map do not support prefix keys; they look up one event at a
time.
search-maptext-mode-maptool-bar-mapview-mode-mapThe following is a list of hook variables that let you provide functions to be called from within Emacs on suitable occasions.
Most of these variables have names ending with ‘-hook’. They are
normal hooks, run by means of run-hooks. The value of such
a hook is a list of functions; the functions are called with no
arguments and their values are completely ignored. The recommended way
to put a new function on such a hook is to call add-hook.
See Hooks, for more information about using hooks.
Every major mode defines a mode hook named
‘modename-mode-hook’. The major mode command runs this
normal hook with run-mode-hooks as the very last thing it does.
See Mode Hooks. Most minor modes have mode hooks too. Mode hooks
are omitted in the list below.
The variables whose names end in ‘-hooks’ or ‘-functions’ are usually abnormal hooks; their values are lists of functions, but these functions are called in a special way (they are passed arguments, or their values are used). The variables whose names end in ‘-function’ have single functions as their values.
A special feature allows you to specify expressions to evaluate if and when a file is loaded (see Hooks for Loading). That feature is not exactly a hook, but does a similar job.
abbrev-expand-functionsactivate-mark-hookafter-change-functionsafter-change-major-mode-hookafter-init-hookafter-insert-file-functionsafter-make-frame-functionsafter-revert-hookafter-save-hookauto-fill-functionauto-save-hookbefore-change-functionsbefore-hack-local-variables-hookbefore-init-hookbefore-make-frame-hookbefore-revert-hookbefore-save-hookblink-paren-functionbuffer-access-fontify-functionscalendar-initial-window-hookcalendar-load-hookcalendar-today-invisible-hookcalendar-today-visible-hookchange-major-mode-hookcommand-line-functionscomment-indent-functioncompilation-finish-functionscustom-define-hookdeactivate-mark-hookdelete-frame-functionsdelete-terminal-functionsdesktop-after-read-hookdesktop-read. May be used
to show a buffer list. See Saving Emacs Sessions.
desktop-no-desktop-file-hookdesktop-read can't find a desktop file.
May be used to show a dired buffer. See Saving Emacs Sessions.
desktop-save-hookdiary-hookdiary-list-entries-hookdiary-mark-entries-hookdiary-nongregorian-listing-hookdiary-nongregorian-marking-hookdiary-print-entries-hookdisabled-command-functionecho-area-clear-hookemacs-startup-hookfind-file-hookfind-file-not-found-functionsfirst-change-hookfont-lock-beginning-of-syntax-functionfont-lock-fontify-buffer-functionfont-lock-fontify-region-functionfont-lock-mark-block-functionfont-lock-syntactic-face-functionfont-lock-unfontify-buffer-functionhack-local-variables-hookfont-lock-unfontify-region-functionkbd-macro-termination-hookkill-buffer-hookkill-buffer-query-functionskill-emacs-hookkill-emacs-query-functionslisp-indent-function
mail-setup-hookmenu-bar-update-hookminibuffer-setup-hookminibuffer-exit-hookmouse-position-functionoccur-hook
post-command-hookpre-command-hookresume-tty-functionsscheme-indent-function
suspend-hooksuspend-resume-hooksuspend-tty-functionstemp-buffer-setup-hooktemp-buffer-show-functiontemp-buffer-show-hookterm-setup-hookwindow-configuration-change-hookwindow-scroll-functionswindow-setup-hookwindow-size-change-functionswrite-contents-functionswrite-file-functionswrite-region-annotate-functions%: Arithmetic Operations&optional: Argument List&rest: Argument List*: Arithmetic Operationsinteractive: Using Interactive+: Arithmetic Operations, (with backquote): Backquote,@ (with backquote): Backquote-: Arithmetic Operations/: Arithmetic Operations/=: Comparison of Numbers1+: Arithmetic Operations1-: Arithmetic Operations1value: Test Coverage2C-mode-map: Prefix Keys<: Comparison of Numbers<=: Comparison of Numbers=: Comparison of Numbers>: Comparison of Numbers>=: Comparison of Numbersinteractive: Using Interactiveinteractive: Using Interactive`: Backquoteabbrev-all-caps: Abbrev Expansionabbrev-expand-functions: Abbrev Expansionabbrev-expansion: Abbrev Expansionabbrev-file-name: Abbrev Filesabbrev-get: Abbrev Propertiesabbrev-insert: Abbrev Expansionabbrev-minor-mode-table-alist: Standard Abbrev Tablesabbrev-mode: Abbrev Modeabbrev-prefix-mark: Abbrev Expansionabbrev-put: Abbrev Propertiesabbrev-start-location: Abbrev Expansionabbrev-start-location-buffer: Abbrev Expansionabbrev-symbol: Abbrev Expansionabbrev-table-get: Abbrev Table Propertiesabbrev-table-name-list: Abbrev Tablesabbrev-table-p: Abbrev Tablesabbrev-table-put: Abbrev Table Propertiesabbreviate-file-name: Directory Namesabbrevs-changed: Abbrev Filesabort-recursive-edit: Recursive Editingabs: Comparison of Numbersaccept-change-group: Atomic Changesaccept-process-output: Accepting Outputaccess-file: Testing Accessibilityaccessible-keymaps: Scanning Keymapsacos: Math Functionsaction (button property): Button Propertiesaction, customization keyword: Type Keywordsactivate-change-group: Atomic Changesactivate-mark-hook: The Markactive-minibuffer-window: Minibuffer Windowsad-activate: Activation of Advicead-activate-all: Activation of Advicead-activate-regexp: Activation of Advicead-add-advice: Computed Advicead-deactivate: Activation of Advicead-deactivate-all: Activation of Advicead-deactivate-regexp: Activation of Advicead-default-compilation-action: Activation of Advicead-define-subr-args: Advising Primitivesad-disable-advice: Enabling Advicead-disable-regexp: Enabling Advicead-do-it: Around-Advicead-enable-advice: Enabling Advicead-enable-regexp: Enabling Advicead-get-arg: Argument Access in Advicead-get-args: Argument Access in Advicead-return-value: Defining Advicead-set-arg: Argument Access in Advicead-set-args: Argument Access in Advicead-start-advice: Activation of Advicead-stop-advice: Activation of Advicead-unadvise: Defining Advicead-unadvise-all: Defining Advicead-update: Activation of Advicead-update-all: Activation of Advicead-update-regexp: Activation of Adviceadaptive-fill-first-line-regexp: Adaptive Filladaptive-fill-function: Adaptive Filladaptive-fill-mode: Adaptive Filladaptive-fill-regexp: Adaptive Filladd-hook: Setting Hooksadd-name-to-file: Changing Filesadd-text-properties: Changing Propertiesadd-to-history: Minibuffer Historyadd-to-invisibility-spec: Invisible Textadd-to-list: List Variablesadd-to-ordered-list: List Variablesadjust-window-trailing-edge: Resizing Windowsafter-change-functions: Change Hooksafter-change-major-mode-hook: Mode Hooksafter-find-file: Subroutines of Visitingafter-init-hook: Init Fileafter-init-time: Startup Summaryafter-insert-file-functions: Format Conversion Piecemealafter-load-alist: Hooks for Loadingafter-load-functions: Hooks for Loadingafter-make-frame-functions: Creating Framesafter-revert-hook: Revertingafter-save-hook: Saving Buffersafter-string (overlay property): Overlay Propertiesall-completions: Basic Completionand: Combining Conditionsappend: Building Listsappend-to-file: Writing to Filesapply: Calling Functionsapply, and debugging: Internals of Debuggerapply-partially: Calling Functionsapropos: Help Functionsapropos-mode-map: Standard Keymapsaref: Array Functionsargs, customization keyword: Composite Typesargv: Command-Line Argumentsarith-error example: Handling Errorsarith-error in division: Arithmetic Operationsarrayp: Array Functionsascii-case-table: Case Tablesaset: Array Functionsash: Bitwise Operationsasin: Math Functionsask-user-about-lock: File Locksask-user-about-supersession-threat: Modification Timeassoc: Association Listsassoc-default: Association Listsassoc-string: Text Comparisonassq: Association Listsassq-delete-all: Association Listsatan: Math Functionsatom: List-related Predicatesauto-coding-alist: Default Coding Systemsauto-coding-functions: Default Coding Systemsauto-coding-regexp-alist: Default Coding Systemsauto-fill-chars: Auto Fillingauto-fill-function: Auto Fillingauto-hscroll-mode: Horizontal Scrollingauto-mode-alist: Auto Major Modeauto-raise-tool-bar-buttons: Tool Barauto-resize-tool-bars: Tool Barauto-save-default: Auto-Savingauto-save-file-name-p: Auto-Savingauto-save-hook: Auto-Savingauto-save-interval: Auto-Savingauto-save-list-file-name: Auto-Savingauto-save-list-file-prefix: Auto-Savingauto-save-mode: Auto-Savingauto-save-timeout: Auto-Savingauto-save-visited-file-name: Auto-Savingauto-window-vscroll: Vertical Scrollingback-to-indentation: Motion by Indentbacktrace: Internals of Debuggerbacktrace-debug: Internals of Debuggerbacktrace-frame: Internals of Debuggerbackup-buffer: Making Backupsbackup-by-copying: Rename or Copybackup-by-copying-when-linked: Rename or Copybackup-by-copying-when-mismatch: Rename or Copybackup-by-copying-when-privileged-mismatch: Rename or Copybackup-directory-alist: Making Backupsbackup-enable-predicate: Making Backupsbackup-file-name-p: Backup Namesbackup-inhibited: Making Backupsbackward-button: Button Buffer Commandsbackward-char: Character Motionbackward-delete-char-untabify: Deletionbackward-delete-char-untabify-method: Deletionbackward-list: List Motionbackward-prefix-chars: Motion and Syntaxbackward-sexp: List Motionbackward-to-indentation: Motion by Indentbackward-word: Word Motionbalance-windows: Resizing Windowsbalance-windows-area: Resizing Windowsbarf-if-buffer-read-only: Read Only Buffersbase64-decode-region: Base 64base64-decode-string: Base 64base64-encode-region: Base 64base64-encode-string: Base 64batch-byte-compile: Compilation Functionsbaud-rate: Terminal Outputbeep: Beepingbefore-change-functions: Change Hooksbefore-hack-local-variables-hook: File Local Variablesbefore-init-hook: Init Filebefore-init-time: Startup Summarybefore-make-frame-hook: Creating Framesbefore-revert-hook: Revertingbefore-save-hook: Saving Buffersbefore-string (overlay property): Overlay Propertiesbeginning-of-buffer: Buffer End Motionbeginning-of-defun: List Motionbeginning-of-defun-function: List Motionbeginning-of-line: Text Linesbinary coding system: Coding System Basicsbindat-get-field: Bindat Functionsbindat-ip-to-string: Bindat Functionsbindat-length: Bindat Functionsbindat-pack: Bindat Functionsbindat-unpack: Bindat Functionsbitmap-spec-p: Face Attributesblink-cursor-alist: Cursor Parametersblink-matching-delay: Blinkingblink-matching-open: Blinkingblink-matching-paren: Blinkingblink-matching-paren-distance: Blinkingblink-paren-function: Blinkingbobp: Near Pointbolp: Near Pointbool-vector-p: Bool-Vectorsbooleanp: nil和tboundp: Void Variablesbuffer-access-fontified-property: Lazy Propertiesbuffer-access-fontify-functions: Lazy Propertiesbuffer-auto-save-file-format: Format Conversion Round-Tripbuffer-auto-save-file-name: Auto-Savingbuffer-backed-up: Making Backupsbuffer-base-buffer: Indirect Buffersbuffer-chars-modified-tick: Buffer Modificationbuffer-disable-undo: Maintaining Undobuffer-display-count: Buffers and Windowsbuffer-display-table: Active Display Tablebuffer-display-time: Buffers and Windowsbuffer-enable-undo: Maintaining Undobuffer-end: Pointbuffer-file-coding-system: Encoding and I/Obuffer-file-format: Format Conversion Round-Tripbuffer-file-name: Buffer File Namebuffer-file-number: Buffer File Namebuffer-file-truename: Buffer File Namebuffer-file-type: MS-DOS File Typesbuffer-has-markers-at: Information from Markersbuffer-invisibility-spec: Invisible Textbuffer-list: The Buffer Listbuffer-live-p: Killing Buffersbuffer-local-value: Creating Buffer-Localbuffer-local-variables: Creating Buffer-LocalBuffer-menu-mode-map: Standard Keymapsbuffer-modified-p: Buffer Modificationbuffer-modified-tick: Buffer Modificationbuffer-name: Buffer Namesbuffer-name-history: Minibuffer Historybuffer-offer-save: Killing Buffersbuffer-read-only: Read Only Buffersbuffer-save-without-query: Killing Buffersbuffer-saved-size: Auto-Savingbuffer-size: Pointbuffer-string: Buffer Contentsbuffer-substring: Buffer Contentsbuffer-substring-filters: Buffer Contentsbuffer-substring-no-properties: Buffer Contentsbuffer-swap-text: Swapping Textbuffer-undo-list: Undobufferp: Buffer Basicsbury-buffer: The Buffer Listbutlast: List Elementsbutton (button property): Button Propertiesbutton-activate: Manipulating Buttonsbutton-at: Manipulating Buttonsbutton-end: Manipulating Buttonsbutton-face, customization keyword: Type Keywordsbutton-get: Manipulating Buttonsbutton-has-type-p: Manipulating Buttonsbutton-label: Manipulating Buttonsbutton-prefix, customization keyword: Type Keywordsbutton-put: Manipulating Buttonsbutton-start: Manipulating Buttonsbutton-suffix, customization keyword: Type Keywordsbutton-type: Manipulating Buttonsbutton-type-get: Manipulating Buttonsbutton-type-put: Manipulating Buttonsbutton-type-subtype-p: Manipulating Buttonsbyte-boolean-vars: Writing Emacs Primitivesbyte-boolean-vars: Variables with Restricted Valuesbyte-code: Compilation Functionsbyte-code-function-p: What Is a Functionbyte-compile: Compilation Functionsbyte-compile-dynamic: Dynamic Loadingbyte-compile-dynamic-docstrings: Docs and Compilationbyte-compile-file: Compilation Functionsrequire: Named Featuresbyte-recompile-directory: Compilation Functionsbyte-to-position: Text Representationsbyte-to-string: Converting RepresentationsC-M-x: Instrumentingc-mode-map: Standard Keymapsc-mode-syntax-table: Standard Syntax TablesC-x X =: Coverage Testingcaar: List Elementscache-long-line-scans: Truncationcadr: List Elementscall-interactively: Interactive Callcall-process: Synchronous Processescall-process, command-line arguments from minibuffer: Shell Argumentscall-process-region: Synchronous Processescall-process-shell-command: Synchronous Processescalled-interactively-p: Distinguish Interactivecancel-change-group: Atomic Changescancel-debug-on-entry: Function Debuggingcancel-timer: Timerscapitalize: Case Conversioncapitalize-region: Case Changescapitalize-word: Case Changescar: List Elementscar-safe: List Elementscase-fold-search: Searching and Casecase-replace: Searching and Casecase-table-p: Case Tablescatch: Catch and Throwcategory (overlay property): Overlay Propertiescategory (text property): Special Propertiescategory-docstring: Categoriescategory-set-mnemonics: Categoriescategory-table: Categoriescategory-table-p: Categoriescdar: List Elementscddr: List Elementscdr: List Elementscdr-safe: List Elementsceiling: Numeric Conversionschange-major-mode-hook: Creating Buffer-Localchar-after: Near Pointchar-before: Near Pointchar-category-set: Categorieschar-charset: Character Setschar-code-property-description: Character Propertieschar-displayable-p: Fontsetschar-equal: Text Comparisonchar-or-string-p: Predicates for Stringschar-property-alias-alist: Examining Propertieschar-script-table: Character Propertieschar-syntax: Syntax Table Functionschar-table-extra-slot: Char-Tableschar-table-p: Char-Tableschar-table-parent: Char-Tableschar-table-range: Char-Tableschar-table-subtype: Char-Tableschar-to-string: String Conversionchar-width: Widthchar-width-table: Character Propertiescharacter quote: Syntax Class Tablecharacterp: Character Codescharset, text property: Explicit Encodingcharset-after: Scanning Charsetscharset-list: Character Setscharset-plist: Character Setscharset-priority-list: Character Setscharsetp: Character Setscheck-coding-system: Lisp and Coding Systemscheck-coding-systems-region: Lisp and Coding Systemscheckdoc-minor-mode: Documentation Tipscl: Lisp历史eq: Comparison of Numbersunion, intersection: Sets And Liststhrow in Emacs: Catch and Throwrplaca vs setcar: Modifying Listsset local: Setting Variablesclear-abbrev-table: Abbrev Tablesclear-image-cache: Image Cacheclear-string: Modifying Stringsclear-this-command-keys: Command Loop Infoclear-visited-file-modtime: Modification Timeclone-indirect-buffer: Indirect Buffersclose parenthesis character: Syntax Class Tableclrhash: Hash Accesscoding-system-aliases: Coding System Basicscoding-system-change-eol-conversion: Lisp and Coding Systemscoding-system-change-text-conversion: Lisp and Coding Systemscoding-system-charset-list: Lisp and Coding Systemscoding-system-eol-type: Lisp and Coding Systemscoding-system-for-read: Specifying Coding Systemscoding-system-for-write: Specifying Coding Systemscoding-system-get: Coding System Basicscoding-system-list: Lisp and Coding Systemscoding-system-p: Lisp and Coding Systemscoding-system-priority-list: Specifying Coding Systemscolor-defined-p: Color Namescolor-gray-p: Color Namescolor-supported-p: Color Namescolor-values: Color Namescombine-after-change-calls: Change Hookscombine-and-quote-strings: Shell Argumentscommand-debug-status: Internals of Debuggercommand-error-function: Processing of Errorscommand-execute: Interactive Callcommand-history: Command Historycommand-history-map: Standard Keymapscommand-line: Command-Line Argumentscommand-line-args: Command-Line Argumentscommand-line-args-left: Command-Line Argumentscommand-line-functions: Command-Line Argumentscommand-line-processed: Command-Line Argumentscommand-remapping: Remapping Commandscommand-switch-alist: Command-Line Argumentscommandp: Interactive Callcommandp example: High-Level Completioncomment ender: Syntax Class Tablecomment starter: Syntax Class Tablecompare-buffer-substrings: Comparing Textcompare-strings: Text Comparisoncompare-window-configurations: Window Configurationscompile-defun: Compilation Functionscompleting-read: Minibuffer Completioncompletion-annotate-function: Programmed Completioncompletion-auto-help: Completion Commandscompletion-boundaries: Basic Completioncompletion-ignore-case: Basic Completioncompletion-ignored-extensions: File Name Completioncompletion-in-region: Basic Completioncompletion-regexp-list: Basic Completioncompletion-styles: Completion Stylescompletion-styles-alist: Completion Stylescompletion-table-dynamic: Programmed Completioncomposition (text property): Special Propertiescomposition property, and point display: Adjusting Pointcompute-motion: Screen Linesconcat: Creating Stringscond: Conditionalscondition-case: Handling Errorscons: Building Listscons-cells-consed: Memory Usageconsp: List-related Predicatesconstrain-to-field: Fieldscontinue-process: Signals to ProcessesControl-X-prefix: Prefix Keyscontrolling-tty-p: Suspending Emacsconvert-standard-filename: Standard File Namescoordinates-in-window-p: Coordinates and Windowscopy-abbrev-table: Abbrev Tablescopy-alist: Association Listscopy-category-table: Categoriescopy-directory: Create/Delete Dirscopy-face: Face Functionscopy-file: Changing Filescopy-hash-table: Other Hashcopy-keymap: Creating Keymapscopy-marker: Creating Markerscopy-overlay: Managing Overlayscopy-region-as-kill: Kill Functionscopy-sequence: Sequence Functionscopy-syntax-table: Syntax Table Functionscopy-tree: Building Listscos: Math Functionscount-lines: Text Linescount-loop: 函数描述示例count-screen-lines: Screen Linescreate-file-buffer: Subroutines of Visitingcreate-fontset-from-fontset-spec: Fontsetscreate-glyph: Glyphscreate-image: Defining Imagesctl-arrow: Usual Displayctl-x-4-map: Prefix Keysctl-x-5-map: Prefix Keysctl-x-map: Prefix Keyscurrent-active-maps: Active Keymapscurrent-buffer: Current Buffercurrent-case-table: Case Tablescurrent-column: Columnscurrent-fill-column: Marginscurrent-frame-configuration: Frame Configurationscurrent-global-map: Controlling Active Mapscurrent-idle-time: Idle Timerscurrent-indentation: Primitive Indentcurrent-input-method: Input Methodscurrent-input-mode: Input Modescurrent-justification: Fillingcurrent-kill: Low-Level Kill Ringcurrent-left-margin: Marginscurrent-local-map: Controlling Active Mapscurrent-message: Displaying Messagescurrent-minor-mode-maps: Controlling Active Mapscurrent-prefix-arg: Prefix Command Argumentscurrent-time: Time of Daycurrent-time-string: Time of Daycurrent-time-zone: Time of Daycurrent-window-configuration: Window Configurationscurrent-word: Buffer Contentscursor (text property): Special Propertiescursor-in-echo-area: Echo Area Customizationcursor-in-non-selected-windows: Cursor Parameterscursor-type: Cursor Parameterscust-print: Printing in Edebugcustom-add-frequent-value: Variable Definitionscustom-reevaluate-setting: Variable Definitionscustomize-package-emacs-version-alist: Common Keywordsdata-directory: Help Functionsdate-leap-year-p: Time Calculationsdate-to-time: Time Parsingdeactivate-mark: The Markdeactivate-mark-hook: The Markdebug: Invoking the Debuggerdebug-ignored-errors: Error Debuggingdebug-on-entry: Function Debuggingdebug-on-error: Error Debuggingdebug-on-error use: Processing of Errorsdebug-on-next-call: Internals of Debuggerdebug-on-quit: Infinite Loopsdebug-on-signal: Error Debuggingdebugger: Internals of Debuggerdebugger-mode-map: Standard Keymapsdeclare: Defining Macrosdeclare-function: Declaring Functionsdecode-char: Character Setsdecode-coding-inserted-region: Explicit Encodingdecode-coding-region: Explicit Encodingdecode-coding-string: Explicit Encodingdecode-time: Time Conversiondef-edebug-spec: Instrumenting Macro Callsdefadvice: Defining Advicedefalias: Defining Functionsdefault-boundp: Default Valuedefault-directory: File Name Expansiondefault-file-modes: Changing Filesdefault-frame-alist: Initial Parametersdefault-input-method: Input Methodsdefault-justification: Fillingdefault-minibuffer-frame: Minibuffers and Framesdefault-process-coding-system: Default Coding Systemsdefault-text-properties: Examining Propertiesdefault-value: Default Valuedefconst: Defining Variablesdefcustom: Variable Definitionsdefface: Defining Facesdefgroup: Group Definitionsdefimage: Defining Imagesdefine-abbrev: Defining Abbrevsdefine-abbrev-table: Abbrev Tablesdefine-button-type: Button Typesdefine-category: Categoriesdefine-derived-mode: Derived Modesdefine-fringe-bitmap: Customizing Bitmapsdefine-generic-mode: Generic Modesdefine-globalized-minor-mode: Defining Minor Modesdefine-hash-table-test: Defining Hashdefine-key: Changing Key Bindingsdefine-key-after: Modifying Menusdefine-minor-mode: Defining Minor Modesdefine-obsolete-face-alias: Face Functionsdefine-obsolete-function-alias: Obsolete Functionsdefine-obsolete-variable-alias: Variable Aliasesdefine-prefix-command: Prefix Keysdefined-colors: Color Namesdefining-kbd-macro: Keyboard Macrosdefmacro: Defining Macrosdefsubr, Lisp symbol for a primitive: Writing Emacs Primitivesdefsubst: Inline Functionsdefun: Defining FunctionsDEFUN, C macro to define Lisp primitives: Writing Emacs Primitivesdefun-prompt-regexp: List Motiondefvar: Defining VariablesDEFVAR_INT, DEFVAR_LISP, DEFVAR_BOOL: Writing Emacs Primitivesdefvaralias: Variable Aliasesdelay-mode-hooks: Mode Hooksdelete: Sets And Listsdelete-and-extract-region: Deletiondelete-auto-save-file-if-necessary: Auto-Savingdelete-auto-save-files: Auto-Savingdelete-backward-char: Deletiondelete-blank-lines: User-Level Deletiondelete-char: Deletiondelete-directory: Create/Delete Dirsdelete-dups: Sets And Listsdelete-exited-processes: Deleting Processesdelete-field: Fieldsdelete-file: Changing Filesdelete-frame: Deleting Framesdelete-frame event: Misc Eventsdelete-frame-functions: Deleting Framesdelete-horizontal-space: User-Level Deletiondelete-indentation: User-Level Deletiondelete-minibuffer-contents: Minibuffer Contentsdelete-old-versions: Numbered Backupsdelete-other-windows: Deleting Windowsdelete-overlay: Managing Overlaysdelete-process: Deleting Processesdelete-region: Deletiondelete-terminal: Multiple Terminalsdelete-terminal-functions: Multiple Terminalsdelete-to-left-margin: Marginsdelete-window: Deleting Windowsdelete-windows-on: Deleting Windowsdelq: Sets And Listsdescribe-bindings: Scanning Keymapsdescribe-buffer-case-table: Case Tablesdescribe-categories: Categoriesdescribe-current-display-table: Display Table Formatdescribe-display-table: Display Table Formatdescribe-mode: Mode Helpdescribe-prefix-bindings: Help Functionsdesktop-buffer-mode-handlers: Desktop Save Modedesktop-save-buffer: Desktop Save Modedestroy-fringe-bitmap: Customizing Bitmapsdetect-coding-region: Lisp and Coding Systemsdetect-coding-string: Lisp and Coding Systemsdigit-argument: Prefix Command Argumentsding: Beepingdir-locals-class-alist: Directory Local Variablesdir-locals-directory-cache: Directory Local Variablesdir-locals-file: Directory Local Variablesdir-locals-set-class-variables: Directory Local Variablesdir-locals-set-directory-class: Directory Local Variablesdirectory-file-name: Directory Namesdirectory-files: Contents of Directoriesdirectory-files-and-attributes: Contents of Directoriesdired-kept-versions: Numbered Backupsdired-mode-map: Standard Keymapsdisable-command: Disabling Commandsdisable-point-adjustment: Adjusting Pointdisabled: Disabling Commandsdisabled-command-function: Disabling Commandsdisassemble: Disassemblydiscard-input: Event Input Miscdisplay (overlay property): Overlay Propertiesdisplay (text property): Display Propertydisplay property, and point display: Adjusting Pointdisplay-backing-store: Display Feature Testingdisplay-buffer: Choosing Windowdisplay-buffer-function: Choosing Windowdisplay-buffer-reuse-frames: Choosing Windowdisplay-color-cells: Display Feature Testingdisplay-color-p: Display Feature Testingdisplay-completion-list: Completion Commandsdisplay-graphic-p: Display Feature Testingdisplay-grayscale-p: Display Feature Testingdisplay-images-p: Display Feature Testingdisplay-message-or-buffer: Displaying Messagesdisplay-mm-dimensions-alist: Display Feature Testingdisplay-mm-height: Display Feature Testingdisplay-mm-width: Display Feature Testingdisplay-mouse-p: Display Feature Testingdisplay-pixel-height: Display Feature Testingdisplay-pixel-width: Display Feature Testingdisplay-planes: Display Feature Testingdisplay-popup-menus-p: Display Feature Testingdisplay-save-under: Display Feature Testingdisplay-screens: Display Feature Testingdisplay-selections-p: Display Feature Testingdisplay-supports-face-attributes-p: Display Feature Testingdisplay-table-slot: Display Table Formatdisplay-visual-class: Display Feature Testingdisplay-warning: Warning Basicsdnd-protocol-alist: Drag and Dropdo-auto-save: Auto-Savingdoc, customization keyword: Type Keywordsdoc-directory: Accessing Documentationdocumentation: Accessing Documentationdocumentation-property: Accessing Documentationdolist: Iterationdotimes: Iterationdotimes-with-progress-reporter: Progressdouble-click-fuzz: Repeat Eventsdouble-click-time: Repeat Eventsdown-list: List Motiondowncase: Case Conversiondowncase-region: Case Changesdowncase-word: Case Changeslookup-key: Key Sequence Inputdrag-n-drop event: Misc Eventsdump-emacs: Building Emacseasy-mmode-define-minor-mode: Defining Minor Modesecho-area-clear-hook: Echo Area Customizationecho-keystrokes: Echo Area Customizationedebug: Source Breakpointsedebug-all-defs: Edebug Optionsedebug-all-forms: Edebug Optionsedebug-continue-kbd-macro: Edebug Optionsedebug-display-freq-count: Coverage Testingedebug-eval-macro-args: Instrumenting Macro Callsedebug-eval-top-level-form: Instrumentingedebug-global-break-condition: Edebug Optionsedebug-initial-mode: Edebug Optionsedebug-on-error: Edebug Optionsedebug-on-quit: Edebug Optionsedebug-print-circle: Printing in Edebugedebug-print-length: Printing in Edebugedebug-print-level: Printing in Edebugedebug-print-trace-after: Trace Bufferedebug-print-trace-before: Trace Bufferedebug-save-displayed-buffer-points: Edebug Optionsedebug-save-windows: Edebug Optionsedebug-set-global-break-condition: Global Break Conditionedebug-setup-hook: Edebug Optionsedebug-sit-for-seconds: Edebug Execution Modesedebug-temp-display-freq-count: Coverage Testingedebug-test-coverage: Edebug Optionsedebug-trace: Edebug Optionsedebug-trace: Trace Bufferedebug-tracing: Trace Bufferedit-abbrevs-map: Standard Keymapsedit-and-eval-command: Object from Minibufferedit-tab-stops-map: Standard Keymapseight-bit, a charset: Character Setselectric-buffer-menu-mode-map: Standard Keymapselectric-future-map: 变量描述示例electric-history-map: Standard Keymapselt: Sequence Functionsemacs, a charset: Character Setsemacs-build-time: 版本信息emacs-init-time: Processor Run Timeemacs-internal coding system: Coding System Basicsemacs-lisp-docstring-fill-column: Documentation Basicsemacs-lisp-mode-map: Standard Keymapsemacs-lisp-mode-syntax-table: Standard Syntax Tablesemacs-major-version: 版本信息emacs-minor-version: 版本信息emacs-pid: System Environmentemacs-save-session-functions: Session Managementemacs-session-restore: Session Managementemacs-startup-hook: Init Fileemacs-uptime: Processor Run Timeemacs-version: 版本信息EMACSLOADPATH environment variable: Library Searchemulation-mode-map-alists: Controlling Active Mapsenable-command: Disabling Commandsenable-local-eval: File Local Variablesenable-local-variables: File Local Variablesenable-multibyte-characters: Text Representationsenable-recursive-minibuffers: Recursive Miniencode-char: Character Setsencode-coding-region: Explicit Encodingencode-coding-string: Explicit Encodingencode-time: Time Conversionend-of-buffer: Buffer End Motionend-of-defun: List Motionend-of-defun-function: List Motionend-of-file: Input Functionsend-of-line: Text Linesenlarge-window: Resizing Windowsenlarge-window-horizontally: Resizing Windowseobp: Near Pointeolp: Near Pointeq: 相等判定eql: Comparison of Numbersequal: 相等判定equal-including-properties: 相等判定erase-buffer: Deletionerror: Signaling Errorserror in debug: Invoking the Debuggererror-conditions: Error Symbolserror-message-string: Handling Errorsesc-map: Prefix KeysESC-prefix: Prefix Keysescape-syntax character: Syntax Class Tableeval: Evaleval, and debugging: Internals of Debuggereval-after-load: Hooks for Loadingeval-and-compile: Eval During Compileeval-at-startup: Building Emacseval-buffer: Evaleval-buffer (Edebug): Instrumentingeval-current-buffer: Evaleval-current-buffer (Edebug): Instrumentingeval-defun (Edebug): Instrumentingeval-expression (Edebug): Instrumentingeval-expression-debug-on-error: Error Debuggingeval-expression-print-length: Output Variableseval-expression-print-level: Output Variableseval-minibuffer: Object from Minibuffereval-region: Evaleval-region (Edebug): Instrumentingeval-when-compile: Eval During Compileevaporate (overlay property): Overlay Propertieseven-window-heights: Choosing Windowevent-basic-type: Classifying Eventsevent-click-count: Repeat Eventsevent-convert-list: Classifying Eventsevent-end: Accessing Mouseevent-modifiers: Classifying Eventsevent-start: Accessing Mouseeventp: Input Eventsewoc-buffer: Abstract Display Functionsewoc-collect: Abstract Display Functionsewoc-create: Abstract Display Functionsewoc-data: Abstract Display Functionsewoc-delete: Abstract Display Functionsewoc-enter-after: Abstract Display Functionsewoc-enter-before: Abstract Display Functionsewoc-enter-first: Abstract Display Functionsewoc-enter-last: Abstract Display Functionsewoc-filter: Abstract Display Functionsewoc-get-hf: Abstract Display Functionsewoc-goto-next: Abstract Display Functionsewoc-goto-node: Abstract Display Functionsewoc-goto-prev: Abstract Display Functionsewoc-invalidate: Abstract Display Functionsewoc-locate: Abstract Display Functionsewoc-location: Abstract Display Functionsewoc-map: Abstract Display Functionsewoc-next: Abstract Display Functionsewoc-nth: Abstract Display Functionsewoc-prev: Abstract Display Functionsewoc-refresh: Abstract Display Functionsewoc-set-data: Abstract Display Functionsewoc-set-hf: Abstract Display Functionsinteractive form: Using Interactiveinteractive: Interactive Examplesexec-directory: Subprocess Creationexec-path: Subprocess Creationexec-suffixes: Subprocess Creationexecutable-find: Locating Filesexecute-extended-command: Interactive Callexecute-kbd-macro: Keyboard Macrosexecuting-kbd-macro: Keyboard Macrosexit: Recursive Editingexit-minibuffer: Minibuffer Commandsexit-recursive-edit: Recursive Editingexp: Math Functionsexpand-abbrev: Abbrev Expansionexpand-file-name: File Name Expansionexpression prefix: Syntax Class Tableexpt: Math Functionsextended-command-history: Minibuffer Historyextra-keyboard-modifiers: Event Modface (button property): Button Propertiesface (overlay property): Overlay Propertiesface (text property): Special Propertiesface-all-attributes: Attribute Functionsface-attribute: Attribute Functionsface-attribute-relative-p: Attribute Functionsface-background: Attribute Functionsface-bold-p: Attribute Functionsface-differs-from-default-p: Face Functionsface-documentation: Face Functionsface-documentation: Accessing Documentationface-equal: Face Functionsface-font: Attribute Functionsface-font-family-alternatives: Font Selectionface-font-registry-alternatives: Font Selectionface-font-rescale-alist: Font Selectionface-font-selection-order: Font Selectionface-foreground: Attribute Functionsface-id: Face Functionsface-inverse-video-p: Attribute Functionsface-italic-p: Attribute Functionsface-list: Face Functionsface-remap-add-relative: Face Remappingface-remap-remove-relative: Face Remappingface-remap-reset-base: Face Remappingface-remap-set-base: Face Remappingface-remapping-alist: Face Remappingface-stipple: Attribute Functionsface-underline-p: Attribute Functionsfacemenu-background-menu: Standard Keymapsfacemenu-face-menu: Standard Keymapsfacemenu-foreground-menu: Standard Keymapsfacemenu-indentation-menu: Standard Keymapsfacemenu-justification-menu: Standard Keymapsfacemenu-keymap: Prefix Keysfacemenu-menu: Standard Keymapsfacemenu-special-menu: Standard Keymapsfacep: Facesfboundp: Function Cellsfceiling: Rounding Operations-unload-function: Unloadingfeaturep: Named Featuresfetch-bytecode: Dynamic Loadingffloor: Rounding Operationsfield (text property): Special Propertiesfield-beginning: Fieldsfield-end: Fieldsfield-string: Fieldsfield-string-no-properties: Fieldsfile-accessible-directory-p: Testing Accessibilityfile-already-exists: Changing Filesfile-attributes: File Attributesfile-chase-links: Truenamesfile-coding-system-alist: Default Coding Systemsfile-directory-p: Kinds of Filesfile-error: How Programs Do Loadingfile-executable-p: Testing Accessibilityfile-exists-p: Testing Accessibilityfile-expand-wildcards: Contents of Directoriesfile-local-copy: Magic File Namesfile-local-variables-alist: File Local Variablesfile-locked: File Locksfile-locked-p: File Locksfile-modes: File Attributesfile-modes-symbolic-to-number: Changing Filesfile-name-absolute-p: Relative File Namesfile-name-all-completions: File Name Completionfile-name-as-directory: Directory Namesfile-name-buffer-file-type-alist: MS-DOS File Typesfile-name-coding-system: Encoding and I/Ofile-name-completion: File Name Completionfile-name-directory: File Name Componentsfile-name-extension: File Name Componentsfile-name-handler-alist: Magic File Namesfile-name-history: Minibuffer Historyfile-name-nondirectory: File Name Componentsfile-name-sans-extension: File Name Componentsfile-name-sans-versions: File Name Componentsfile-newer-than-file-p: Testing Accessibilityfile-newest-backup: Backup Namesfile-nlinks: File Attributesfile-ownership-preserved-p: Testing Accessibilityfile-precious-flag: Saving Buffersfile-readable-p: Testing Accessibilityfile-regular-p: Kinds of Filesfile-relative-name: Relative File Namesfile-remote-p: Magic File Namesfile-supersession: Modification Timefile-symlink-p: Kinds of Filesfile-truename: Truenamesfile-writable-p: Testing Accessibilityfill-column: Marginsfill-context-prefix: Adaptive Fillfill-forward-paragraph-function: Fillingfill-individual-paragraphs: Fillingfill-individual-varying-indent: Fillingfill-nobreak-predicate: Marginsfill-paragraph: Fillingfill-paragraph-function: Fillingfill-prefix: Marginsfill-region: Fillingfill-region-as-paragraph: Fillingfillarray: Array Functionsfilter-buffer-substring: Buffer Contentsfind-auto-coding: Default Coding Systemsfind-backup-file-name: Backup Namesfind-buffer-visiting: Buffer File Namefind-charset-region: Scanning Charsetsfind-charset-string: Scanning Charsetsfind-coding-systems-for-charsets: Lisp and Coding Systemsfind-coding-systems-region: Lisp and Coding Systemsfind-coding-systems-string: Lisp and Coding Systemsfind-file: Visiting Functionsfind-file-hook: Visiting Functionsfind-file-literally: Visiting Functionsfind-file-name-handler: Magic File Namesfind-file-noselect: Visiting Functionsfind-file-not-found-functions: Visiting Functionsfind-file-other-window: Visiting Functionsfind-file-read-only: Visiting Functionsfind-file-wildcards: Visiting Functionsfind-font: Low-Level Fontfind-image: Defining Imagesfind-operation-coding-system: Default Coding Systemsfirst-change-hook: Change Hooksfit-window-to-buffer: Resizing Windowsfixup-whitespace: User-Level Deletionfloat: Numeric Conversionsfloat-e: Float Basicsfloat-output-format: Output Variablesfloat-pi: Float Basicsfloat-time: Time of Dayfloatp: Predicates on Numbersfloats-consed: Memory Usagefloor: Numeric Conversionsfmakunbound: Function Cellsfn in function's documentation string: Autoloadfocus-follows-mouse: Input Focusfollow-link (button property): Button Propertiesfollowing-char: Near Pointfont-at: Low-Level Fontfont-face-attributes: Low-Level Fontfont-family-list: Face Attributesfont-get: Low-Level Fontfont-list-limit: Font Lookupfont-lock-add-keywords: Customizing Keywordsfont-lock-beginning-of-syntax-function: Syntactic Font Lockfont-lock-builtin-face: Faces for Font Lockfont-lock-comment-delimiter-face: Faces for Font Lockfont-lock-comment-face: Faces for Font Lockfont-lock-constant-face: Faces for Font Lockfont-lock-defaults: Font Lock Basicsfont-lock-doc-face: Faces for Font Lockfont-lock-extend-after-change-region-function: Region to Fontifyfont-lock-extra-managed-props: Other Font Lock Variablesfont-lock-face (text property): Special Propertiesfont-lock-fontify-buffer-function: Other Font Lock Variablesfont-lock-fontify-region-function: Other Font Lock Variablesfont-lock-function-name-face: Faces for Font Lockfont-lock-keyword-face: Faces for Font Lockfont-lock-keywords: Search-based Fontificationfont-lock-keywords-case-fold-search: Search-based Fontificationfont-lock-keywords-only: Syntactic Font Lockfont-lock-mark-block-function: Other Font Lock Variablesfont-lock-multiline: Font Lock Multilinefont-lock-negation-char-face: Faces for Font Lockfont-lock-preprocessor-face: Faces for Font Lockfont-lock-remove-keywords: Customizing Keywordsfont-lock-string-face: Faces for Font Lockfont-lock-syntactic-face-function: Syntactic Font Lockfont-lock-syntactic-keywords: Setting Syntax Propertiesfont-lock-syntax-table: Syntactic Font Lockfont-lock-type-face: Faces for Font Lockfont-lock-unfontify-buffer-function: Other Font Lock Variablesfont-lock-unfontify-region-function: Other Font Lock Variablesfont-lock-variable-name-face: Faces for Font Lockfont-lock-warning-face: Faces for Font Lockfont-put: Low-Level Fontfont-spec: Low-Level Fontfont-xlfd-name: Low-Level Fontfontification-functions: Auto Facesfontified (text property): Special Propertiesfontp: Low-Level Fontfoo: 函数描述示例for: Argument Evaluationforce-mode-line-update: Mode Line Basicsforce-window-update: Forcing Redisplayformat: Formatting Stringsformat, customization keyword: Type Keywordsformat-alist: Format Conversion Round-Tripformat-find-file: Format Conversion Round-Tripformat-insert-file: Format Conversion Round-Tripformat-mode-line: Emulating Mode Lineformat-network-address: Misc Networkformat-seconds: Time Parsingformat-time-string: Time Parsingformat-write-file: Format Conversion Round-Tripforward-button: Button Buffer Commandsforward-char: Character Motionforward-comment: Motion via Parsingforward-line: Text Linesforward-list: List Motionforward-sexp: List Motionforward-to-indentation: Motion by Indentforward-word: Word Motionframe-alpha-lower-limit: Font and Color Parametersframe-background-mode: Defining Facesframe-char-height: Size and Positionframe-char-width: Size and Positionframe-current-scroll-bars: Scroll Barsframe-first-window: Frames and Windowsframe-height: Size and Positionframe-inherited-parameters: Creating Framesframe-list: Finding All Framesframe-live-p: Deleting Framesframe-parameter: Parameter Accessframe-parameters: Parameter Accessframe-pixel-height: Size and Positionframe-pixel-width: Size and Positionframe-selected-window: Frames and Windowsframe-terminal: Framesframe-title-format: Frame Titlesframe-visible-p: Visibility of Framesframe-width: Size and Positionframep: Framesfringe-bitmaps-at-pos: Fringe Bitmapsfringe-cursor-alist: Fringe Cursorsfringe-indicator-alist: Fringe Indicatorsfringes-outside-margins: Fringe Size/Posfround: Rounding Operationsfset: Function Cellsftp-login: Cleanupsftruncate: Rounding Operationsfuncall: Calling Functionsfuncall, and debugging: Internals of Debuggerfunction: Anonymous Functionsfunction-documentation: Documentation Basicsfunctionp: What Is a Functionfundamental-mode: Auto Major Modefundamental-mode-abbrev-table: Standard Abbrev Tablesfundamental-mode-map: Standard Keymapsgap-position: Buffer Gapgap-size: Buffer Gapgarbage-collect: Garbage Collectiongarbage-collection-messages: Garbage Collectiongc-cons-percentage: Garbage Collectiongc-cons-threshold: Garbage Collectiongc-elapsed: Garbage CollectionGCPRO and UNGCPRO: Writing Emacs Primitivesgcs-done: Garbage Collectiongenerate-autoload-cookie: Autoloadgenerate-new-buffer: Creating Buffersgenerate-new-buffer-name: Buffer Namesgenerated-autoload-file: Autoloadgeneric comment delimiter: Syntax Class Tablegeneric string delimiter: Syntax Class Tableget: Symbol Plistsget, defcustom keyword: Variable Definitionsget-buffer: Buffer Namesget-buffer-create: Creating Buffersget-buffer-process: Process Buffersget-buffer-window: Buffers and Windowsget-buffer-window-list: Buffers and Windowsget-byte: Character Codesget-char-code-property: Character Propertiesget-char-property: Examining Propertiesget-char-property-and-overlay: Examining Propertiesget-charset-property: Character Setsget-device-terminal: Multiple Terminalsget-file-buffer: Buffer File Nameget-file-char: Input Streamsget-internal-run-time: Processor Run Timeget-largest-window: Selecting Windowsget-load-suffixes: Load Suffixesget-lru-window: Selecting Windowsget-process: Process Informationget-register: Registersget-text-property: Examining Propertiesget-unused-category: Categoriesget-window-with-predicate: Selecting Windowsgetenv: System Environmentgethash: Hash Accessglobal-abbrev-table: Standard Abbrev Tablesglobal-disable-point-adjustment: Adjusting Pointglobal-key-binding: Functions for Key Lookupglobal-map: Controlling Active Mapsglobal-mode-string: Mode Line Variablesglobal-set-key: Key Binding Commandsglobal-unset-key: Key Binding Commandsglyph-char: Glyphsglyph-face: Glyphsglyph-table: Glyphsgoto-char: Character Motiongoto-map: Prefix Keysgrep-mode-map: Standard Keymapsgroup, customization keyword: Common Keywordshack-dir-local-variables: Directory Local Variableshack-local-variables: File Local Variableshack-local-variables-hook: File Local Variableshandle-shift-selection: The Markhandle-switch-frame: Input Focushash-table-count: Other Hashhash-table-p: Other Hashhash-table-rehash-size: Other Hashhash-table-rehash-threshold: Other Hashhash-table-size: Other Hashhash-table-test: Other Hashhash-table-weakness: Other Hashheader-line prefix key: Key Sequence Inputheader-line-format: Header Lineshelp-buffer: Help Functionshelp-char: Help Functionshelp-command: Help Functionshelp-echo (overlay property): Overlay Propertieshelp-echo (text property): Special Propertieshelp-echo event: Misc Eventshelp-echo, customization keyword: Type Keywordshelp-event-list: Help Functionshelp-form: Help Functionshelp-index (button property): Button Propertieshelp-map: Help Functionshelp-mode-map: Standard Keymapshelp-setup-xref: Help FunctionsHelper-describe-bindings: Help FunctionsHelper-help: Help FunctionsHelper-help-map: Standard Keymapshistory-add-new-input: Minibuffer Historyhistory-delete-duplicates: Minibuffer Historyhistory-length: Minibuffer HistoryHOME environment variable: Subprocess Creationhorizontal-scroll-bar prefix key: Key Sequence Inputicon-title-format: Frame Titlesiconify-frame: Visibility of Framesiconify-frame event: Misc Eventsidentity: Calling Functionsif: Conditionalsignore: Calling Functionsignore-errors: Handling Errorsignored-local-variables: File Local Variablesimage-cache-eviction-delay: Image Cacheimage-library-alist: Image Formatsimage-load-path: Defining Imagesimage-load-path-for-library: Defining Imagesimage-mask-p: Image Descriptorsimage-refresh: Image Cacheimage-size: Showing Imagesimage-type-available-p: Image Formatsimage-types: Image Formatsimenu-add-to-menubar: Imenuimenu-case-fold-search: Imenuimenu-create-index-function: Imenuimenu-extract-index-name-function: Imenuimenu-generic-expression: Imenuimenu-prev-index-position-function: Imenuimenu-syntax-alist: Imenuprogn: Sequencinginc: Simple Macroindent-according-to-mode: Mode-Specific Indentindent-code-rigidly: Region Indentindent-for-tab-command: Mode-Specific Indentindent-line-function: Mode-Specific Indentindent-region: Region Indentindent-region-function: Region Indentindent-relative: Relative Indentindent-relative-maybe: Relative Indentindent-rigidly: Region Indentindent-tabs-mode: Primitive Indentindent-to: Primitive Indentindent-to-left-margin: Marginsindicate-buffer-boundaries: Fringe Indicatorsindicate-empty-lines: Fringe Indicatorsindirect-function: Function Indirectionindirect-variable: Variable AliasesInfo-edit-map: Standard KeymapsInfo-mode-map: Standard Keymapsinherit standard syntax: Syntax Class Tableinhibit-default-init: Init Fileinhibit-eol-conversion: Specifying Coding Systemsinhibit-field-text-motion: Word Motioninhibit-file-name-handlers: Magic File Namesinhibit-file-name-operation: Magic File Namesinhibit-iso-escape-detection: Lisp and Coding Systemsinhibit-modification-hooks: Change Hooksinhibit-null-byte-detection: Lisp and Coding Systemsinhibit-point-motion-hooks: Special Propertiesinhibit-quit: Quittinginhibit-read-only: Read Only Buffersinhibit-splash-screen: Startup Summaryinhibit-startup-echo-area-message: Startup Summaryinhibit-startup-message: Startup Summaryinhibit-startup-screen: Startup Summaryinhibit-x-resources: Resourcesinit-file-user: User Identificationinitial-buffer-choice: Startup Summaryinitial-environment: System Environmentinitial-frame-alist: Initial Parametersinitial-major-mode: Auto Major Modeinitial-scratch-message: Startup Summaryinitial-window-system: Window Systemsinitial-window-system, and startup: Startup Summaryinitialize, defcustom keyword: Variable Definitionsinput-decode-map: Translation Keymapsinput-method-alist: Input Methodsinput-method-function: Invoking the Input Methodinput-pending-p: Event Input Miscinsert: Insertioninsert-abbrev-table-description: Abbrev Tablesinsert-and-inherit: Sticky Propertiesinsert-before-markers: Insertioninsert-before-markers-and-inherit: Sticky Propertiesinsert-behind-hooks (overlay property): Overlay Propertiesinsert-behind-hooks (text property): Special Propertiesinsert-buffer: Commands for Insertioninsert-buffer-substring: Insertioninsert-buffer-substring-as-yank: Yankinginsert-buffer-substring-no-properties: Insertioninsert-button: Making Buttonsinsert-char: Insertioninsert-default-directory: Reading File Namesinsert-directory: Contents of Directoriesinsert-directory-program: Contents of Directoriesinsert-file-contents: Reading from Filesinsert-file-contents-literally: Reading from Filesinsert-for-yank: Yankinginsert-image: Showing Imagesinsert-in-front-hooks (overlay property): Overlay Propertiesinsert-in-front-hooks (text property): Special Propertiesinsert-register: Registersinsert-sliced-image: Showing Imagesinsert-text-button: Making Buttonsinstallation-directory: System Environmentintangible (overlay property): Overlay Propertiesintangible (text property): Special Propertiesinteger-or-marker-p: Predicates on Markersintegerp: Predicates on Numbersinteractive: Using Interactiveinteractive, examples of using: Interactive Examplesinteractive-form: Using Interactiveinteractive-form, function property: Using Interactiveintern: Creating Symbolsintern-soft: Creating Symbolsinterpreter-mode-alist: Auto Major Modeinterprogram-cut-function: Low-Level Kill Ringinterprogram-paste-function: Low-Level Kill Ringinterrupt-process: Signals to Processesintervals-consed: Memory Usageinvalid-function: Function Indirectioninvalid-regexp: Regexp Backslashinvert-face: Attribute Functionsinvisible (overlay property): Overlay Propertiesinvisible (text property): Special Propertiesinvisible-p: Invisible Textinvocation-directory: System Environmentinvocation-name: System Environmentisearch-mode-map: Standard Keymapsjit-lock-register: Other Font Lock Variablesjit-lock-unregister: Other Font Lock Variablesjust-one-space: User-Level Deletionjustify-current-line: Fillingkbd: Key Sequenceskbd-macro-termination-hook: Keyboard Macroskept-new-versions: Numbered Backupskept-old-versions: Numbered Backupskey-binding: Active Keymapskey-description: Describing Characterskey-translation-map: Translation Keymapskeyboard-coding-system: Terminal I/O Encodingkeyboard-quit: Quittingkeyboard-translate: Event Modkeyboard-translate-table: Event Modkeymap (button property): Button Propertieskeymap (overlay property): Overlay Propertieskeymap (text property): Special Propertieskeymap-parent: Inheritance and Keymapskeymap-prompt: Defining Menuskeymapp: Format of Keymapskeywordp: Constant Variableskill-all-local-variables: Creating Buffer-Localkill-append: Low-Level Kill Ringkill-buffer: Killing Bufferskill-buffer-hook: Killing Bufferskill-buffer-query-functions: Killing Bufferskill-emacs: Killing Emacskill-emacs-hook: Killing Emacskill-emacs-query-functions: Killing Emacskill-local-variable: Creating Buffer-Localkill-new: Low-Level Kill Ringkill-process: Signals to Processeskill-read-only-ok: Kill Functionskill-region: Kill Functionskill-ring: Internals of Kill Ringkill-ring-max: Internals of Kill Ringkill-ring-yank-pointer: Internals of Kill Ringkmacro-map: Standard Keymapslambda in debug: Invoking the Debuggerlambda in keymap: Key Lookuplast: List Elementslast-abbrev: Abbrev Expansionlast-abbrev-location: Abbrev Expansionlast-abbrev-text: Abbrev Expansionlast-buffer: The Buffer Listlast-coding-system-used: Encoding and I/Olast-command: Command Loop Infolast-command-char: Command Loop Infolast-command-event: Command Loop Infolast-event-frame: Command Loop Infolast-input-char: Event Input Misclast-input-event: Event Input Misclast-kbd-macro: Keyboard Macroslast-nonmenu-event: Command Loop Infolast-prefix-arg: Prefix Command Argumentslast-repeatable-command: Command Loop Infolax-plist-get: Other Plistslax-plist-put: Other Plistslazy-completion-table: Basic Completionleft-fringe-width: Fringe Size/Posleft-margin: Marginsleft-margin-width: Display Marginslength: Sequence Functionslet: Local Variableslet*: Local Variablesline-beginning-position: Text Linesline-end-position: Text Linesline-height (text property): Line Heightline-height (text property): Special Propertiesline-move-ignore-invisible: Invisible Textline-number-at-pos: Text Linesline-prefix: Truncationline-spacing: Line Heightline-spacing (text property): Line Heightline-spacing (text property): Special Propertieslink, customization keyword: Common Keywordslisp-interaction-mode-map: Standard Keymapslisp-mode-abbrev-table: Standard Abbrev Tableslisp-mode-map: Standard Keymapslist: Building Listslist-buffers-directory: Buffer File Namelist-charset-chars: Character Setslist-fonts: Low-Level Fontlist-load-path-shadows: Library Searchlist-processes: Process Informationlist-system-processes: System Processeslistify-key-sequence: Event Input Misclistp: List-related Predicatesln: Changing Filesload: How Programs Do Loadingload, customization keyword: Common Keywordsload-average: System Environmentload-file: How Programs Do Loadingload-file-name: How Programs Do Loadingload-file-rep-suffixes: Load Suffixesload-history: Where Definedload-in-progress: How Programs Do Loadingload-library: How Programs Do Loadingload-path: Library Searchload-read-function: How Programs Do Loadingload-suffixes: Load Suffixeslocal-abbrev-table: Standard Abbrev Tableslocal-function-key-map: Translation Keymapslocal-key-binding: Functions for Key Lookuplocal-map (overlay property): Overlay Propertieslocal-map (text property): Special Propertieslocal-set-key: Key Binding Commandslocal-unset-key: Key Binding Commandslocal-variable-if-set-p: Creating Buffer-Locallocal-variable-p: Creating Buffer-Locallocale-coding-system: Localeslocale-info: Localeslocate-file: Locating Fileslocate-library: Library Searchlock-buffer: File Lockslog: Math Functionslog10: Math Functionslogand: Bitwise Operationslogb: Float Basicslogior: Bitwise Operationslognot: Bitwise Operationslogxor: Bitwise Operationslooking-at: Regexp Searchlooking-at-p: Regexp Searchlooking-back: Regexp Searchlookup-key: Functions for Key Lookuplower-frame: Raising and Loweringlsh: Bitwise Operationslwarn: Warning Basicsmacroexpand: Expansionmacroexpand-all: Expansionmagic-fallback-mode-alist: Auto Major Modemagic-mode-alist: Auto Major Modemail-host-address: System Environmentmajor-mode: Mode Helpmajor-mode: Auto Major Modemake-abbrev-table: Abbrev Tablesmake-auto-save-file-name: Auto-Savingmake-backup-file-name: Backup Namesmake-backup-file-name-function: Making Backupsmake-backup-files: Making Backupsmake-bool-vector: Bool-Vectorsmake-button: Making Buttonsmake-byte-code: Byte-Code Objectsmake-category-set: Categoriesmake-category-table: Categoriesmake-char-table: Char-Tablesmake-directory: Create/Delete Dirsmake-display-table: Display Table Formatmake-face: Face Functionsmake-frame: Creating Framesmake-frame-invisible: Visibility of Framesmake-frame-on-display: Multiple Terminalsmake-frame-visible: Visibility of Framesmake-frame-visible event: Misc Eventsmake-glyph-code: Glyphsmake-hash-table: Creating Hashmake-help-screen: Help Functionsmake-indirect-buffer: Indirect Buffersmake-keymap: Creating Keymapsmake-list: Building Listsmake-local-variable: Creating Buffer-Localmake-marker: Creating Markersmake-network-process: Network Processesmake-obsolete: Obsolete Functionsmake-obsolete-variable: Variable Aliasesmake-overlay: Managing Overlaysmake-progress-reporter: Progressmake-ring: Ringsmake-serial-process: Serial Portsmake-sparse-keymap: Creating Keymapsmake-string: Creating Stringsmake-symbol: Creating Symbolsmake-symbolic-link: Changing Filesmake-syntax-table: Syntax Table Functionsmake-temp-file: Unique File Namesmake-temp-name: Unique File Namesmake-text-button: Making Buttonsmake-translation-table: Translation of Charactersmake-translation-table-from-alist: Translation of Charactersmake-translation-table-from-vector: Translation of Charactersmake-variable-buffer-local: Creating Buffer-Localmake-vector: Vector Functionsmakehash: Creating Hashmakunbound: Void Variablesmap-char-table: Char-Tablesmap-charset-chars: Character Setsmap-keymap: Scanning Keymapsmap-y-or-n-p: Multiple Queriesmapatoms: Creating Symbolsmapc: Mapping Functionsmapcar: Mapping Functionsmapconcat: Mapping Functionsmaphash: Hash Accessmark: The Markmark-active: The Markmark-even-if-inactive: The Markmark-marker: The Markmark-ring: The Markmark-ring-max: The Markmarker-buffer: Information from Markersmarker-insertion-type: Marker Insertion Typesmarker-position: Information from Markersmarkerp: Predicates on Markersmatch, customization keyword: Type Keywordsmatch-alternatives, customization keyword: Composite Typesmatch-beginning: Simple Match Datamatch-data: Entire Match Datamatch-end: Simple Match Datamatch-string: Simple Match Datamatch-string-no-properties: Simple Match Datamatch-substitute-replacement: Replacing Matchmax: Comparison of Numbersmax-char: Character Codesmax-image-size: Showing Imagesmax-lisp-eval-depth: Evalmax-mini-window-height: Minibuffer Miscmax-specpdl-size: Local Variablesmd5: MD5 Checksummember: Sets And Listsmember-ignore-case: Sets And Listsmemory-full: Garbage Collectionmemory-limit: Garbage Collectionmemory-use-counts: Garbage Collectionmemq: Sets And Listsmemql: Sets And Listsmenu-bar prefix key: Key Sequence Inputmenu-bar-edit-menu: Standard Keymapsmenu-bar-file-menu: Standard Keymapsmenu-bar-final-items: Menu Barmenu-bar-help-menu: Standard Keymapsmenu-bar-mule-menu: Standard Keymapsmenu-bar-search-menu: Standard Keymapsmenu-bar-tools-menu: Standard Keymapsmenu-bar-update-hook: Menu Barmenu-item: Extended Menu Itemsmenu-prompt-more-char: Keyboard Menusmerge-face-attribute: Attribute Functionsmessage: Displaying 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Parametersminibuffer-help-form: Minibuffer Miscminibuffer-history: Minibuffer Historyminibuffer-local-completion-map: Completion Commandsminibuffer-local-filename-completion-map: Completion Commandsminibuffer-local-filename-must-match-map: Completion Commandsminibuffer-local-map: Text from Minibufferminibuffer-local-must-match-map: Completion Commandsminibuffer-local-ns-map: Text from Minibufferminibuffer-local-shell-command-map: Reading File Namesminibuffer-message: Minibuffer Miscminibuffer-prompt: Minibuffer Contentsminibuffer-prompt-end: Minibuffer Contentsminibuffer-prompt-width: Minibuffer Contentsminibuffer-scroll-window: Minibuffer Miscminibuffer-selected-window: Minibuffer Miscminibuffer-setup-hook: Minibuffer Miscminibuffer-window: Minibuffer Windowsminibuffer-window-active-p: Minibuffer Windowsminibufferp: Minibuffer Miscminor-mode-alist: Mode Line Variablesminor-mode-key-binding: Functions for Key Lookupminor-mode-list: Minor Modesminor-mode-map-alist: Controlling Active Mapsminor-mode-overriding-map-alist: Controlling Active Mapsmisc-objects-consed: Memory Usagemkdir: Create/Delete Dirsmod: Arithmetic Operationsmode-class (property): Major Mode Conventionsmode-line prefix key: Key Sequence Inputmode-line-buffer-identification: Mode Line Variablesmode-line-format: Mode Line Topmode-line-frame-identification: Mode Line Variablesmode-line-modes: Mode Line Variablesmode-line-modified: Mode Line Variablesmode-line-mule-info: Mode Line Variablesmode-line-position: Mode Line Variablesmode-line-process: Mode Line Variablesmode-name: Mode Line Variablesmode-specific-map: Prefix Keysmodification-hooks (overlay property): Overlay Propertiesmodification-hooks (text property): Special Propertiesmodify-all-frames-parameters: Parameter Accessmodify-category-entry: Categoriesmodify-frame-parameters: Parameter Accessmodify-syntax-entry: Syntax Table Functionsmomentary-string-display: Temporary Displaysmost-negative-fixnum: Integer Basicsmost-positive-fixnum: Integer Basicsmouse-1-click-follows-link: Clickable Textmouse-action (button property): Button Propertiesmouse-face (button property): Button Propertiesmouse-face (overlay property): Overlay Propertiesmouse-face (text property): Special Propertiesmouse-movement-p: Classifying Eventsmouse-on-link-p: Clickable Textmouse-pixel-position: Mouse Positionmouse-position: Mouse Positionmouse-position-function: Mouse Positionmouse-wheel-down-event: Misc Eventsmouse-wheel-up-event: Misc Eventsmove-marker: Moving Markersmove-overlay: Managing Overlaysmove-to-column: Columnsmove-to-left-margin: Marginsmove-to-window-line: Screen Linesmovemail: Subprocess Creationmule-keymap: Prefix Keysmulti-query-replace-map: Search and Replacemultibyte-char-to-unibyte: Converting Representationsmultibyte-string-p: Text Representationsmultibyte-syntax-as-symbol: Control Parsingmultiple-frames: Frame Titlesnarrow-to-page: Narrowingnarrow-to-region: Narrowingnatnump: Predicates on Numbersnbutlast: List Elementsnconc: Rearrangementnegative-argument: Prefix Command Argumentsnetwork-coding-system-alist: Default Coding Systemsnetwork-interface-info: Misc Networknetwork-interface-list: Misc Networknewline: Commands for Insertionnewline-and-indent: Mode-Specific Indentnext-button: Button Buffer Commandsnext-char-property-change: Property Searchnext-frame: Finding All Framesnext-history-element: Minibuffer Commandsnext-matching-history-element: Minibuffer Commandsnext-overlay-change: Finding Overlaysnext-property-change: Property Searchnext-screen-context-lines: Textual Scrollingnext-single-char-property-change: Property Searchnext-single-property-change: Property Searchnext-window: Cyclic Window Orderingnil: nil和tnil in keymap: Key Lookupnil input stream: Input Streamsnil output stream: Output Streamsnlistp: List-related Predicatesno-byte-compile: Byte Compilationno-catch: Catch and Throwno-conversion coding system: Coding System Basicsno-redraw-on-reenter: Refresh Screenno-self-insert property: Defining Abbrevsnoninteractive: Batch Modenoreturn: Test Coveragenormal-auto-fill-function: Auto Fillingnormal-backup-enable-predicate: Making Backupsnormal-mode: Auto Major Modenot: Combining Conditionsnot-modified: Buffer Modificationnreverse: Rearrangementnth: List Elementsnthcdr: List Elementsnull: List-related Predicatesnum-input-keys: Key Sequence Inputnum-nonmacro-input-events: Reading One Eventnumber-or-marker-p: Predicates on Markersnumber-sequence: Building Listsnumber-to-string: String Conversionnumberp: Predicates on Numbersoccur-mode-map: Standard Keymapsone-window-p: Splitting Windowsonly-global-abbrevs: Defining Abbrevsopen parenthesis character: Syntax Class Tableopen-dribble-file: Recording Inputopen-network-stream: Networkopen-paren-in-column-0-is-defun-start: List Motionopen-termscript: Terminal Outputoperations (property): Magic File Namesoptions, defcustom keyword: Variable Definitionsor: Combining Conditionsother-buffer: The Buffer Listother-window: Cyclic Window Orderingother-window-scroll-buffer: Textual Scrollingoverflow-newline-into-fringe: Fringe Cursorsoverlay-arrow-position: Overlay Arrowoverlay-arrow-string: Overlay Arrowoverlay-arrow-variable-list: Overlay Arrowoverlay-buffer: Managing Overlaysoverlay-end: Managing Overlaysoverlay-get: Overlay Propertiesoverlay-properties: Overlay Propertiesoverlay-put: Overlay Propertiesoverlay-recenter: Managing Overlaysoverlay-start: Managing Overlaysoverlayp: Managing Overlaysoverlays-at: Finding Overlaysoverlays-in: Finding Overlaysoverriding-local-map: Controlling Active Mapsoverriding-local-map-menu-flag: Controlling Active Mapsoverriding-terminal-local-map: Controlling Active Mapsoverwrite-mode: Commands for Insertionpackage-version, customization keyword: Common Keywordspage-delimiter: Standard Regexpspaired delimiter: Syntax Class Tableparagraph-separate: Standard Regexpsparagraph-start: Standard Regexpsparse-colon-path: System Environmentparse-partial-sexp: Low-Level 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Regexpsposix-search-backward: POSIX Regexpsposix-search-forward: POSIX Regexpsposix-string-match: POSIX Regexpsposn-actual-col-row: Accessing Mouseposn-area: Accessing Mouseposn-at-point: Accessing Mouseposn-at-x-y: Accessing Mouseposn-col-row: Accessing Mouseposn-image: Accessing Mouseposn-object: Accessing Mouseposn-object-width-height: Accessing Mouseposn-object-x-y: Accessing Mouseposn-point: Accessing Mouseposn-string: Accessing Mouseposn-timestamp: Accessing Mouseposn-window: Accessing Mouseposn-x-y: Accessing Mousepost-command-hook: Command Overviewpost-gc-hook: Garbage Collectionpre-command-hook: Command Overviewpreceding-char: Near Pointprefix, defgroup keyword: Group Definitionsprefix-arg: Prefix Command Argumentsprefix-help-command: Help Functionsprefix-numeric-value: Prefix Command Argumentspreloaded-file-list: Building Emacsprepare-change-group: Atomic Changesprevious-button: Button Buffer Commandsprevious-char-property-change: Property Searchprevious-frame: Finding All Framesprevious-history-element: Minibuffer Commandsprevious-matching-history-element: Minibuffer Commandsprevious-overlay-change: Finding Overlaysprevious-property-change: Property Searchprevious-single-char-property-change: Property Searchprevious-single-property-change: Property Searchprevious-window: Cyclic Window Orderingprimitive-undo: Undoprin1: Output Functionsprin1-to-string: Output Functionsprinc: Output Functionsprint: Output Functionsprint-circle: Output Variablesprint-continuous-numbering: Output Variablesprint-escape-multibyte: Output Variablesprint-escape-newlines: Output Variablesprint-escape-nonascii: Output Variablesprint-gensym: Output Variablesprint-length: Output Variablesprint-level: Output Variablesprint-number-table: Output Variablesprint-quoted: Output Variablesprintable-chars: Character Propertiespriority (overlay property): Overlay Propertiesprocess-adaptive-read-buffering: Output from Processesprocess-attributes: System Processesprocess-buffer: Process 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Input to Processesprocess-send-string: Input to Processesprocess-sentinel: Sentinelsprocess-status: Process Informationprocess-tty-name: Process Informationprocess-type: Process Informationprocessp: Processesprog1: Sequencingprog2: Sequencingprogn: Sequencingprogress-reporter-done: Progressprogress-reporter-force-update: Progressprogress-reporter-update: Progresspropertize: Changing Propertiesprovide: Named Featurespunctuation character: Syntax Class Tablepure-bytes-used: Pure Storagepurecopy: Pure Storagepurify-flag: Pure Storagepush: List Variablespush-button: Button Buffer Commandspush-mark: The Markput: Symbol Plistsput-char-code-property: Character Propertiesput-charset-property: Character Setsput-image: Showing Imagesput-text-property: Changing Propertiesputhash: Hash Accessquery-replace-history: Minibuffer Historyquery-replace-map: Search and Replacequietly-read-abbrev-file: Abbrev Filesquit-flag: Quittingquit-process: Signals to Processesquote: Quotingquoted-insert suppression: Changing Key Bindingsraise-frame: Raising and Loweringrandom: Random Numbersrassoc: Association Listsrassq: Association Listsrassq-delete-all: Association Listsraw-text coding system: Coding System Basicsre-builder: Regular Expressionsre-search-backward: Regexp Searchre-search-forward: Regexp Searchread: Input Functionsread-buffer: High-Level Completionread-buffer-completion-ignore-case: High-Level Completionread-buffer-function: High-Level Completionread-char: Reading One Eventread-char-exclusive: Reading One Eventread-circle: Input Functionsread-coding-system: User-Chosen Coding Systemsread-color: High-Level Completionread-command: High-Level Completionread-directory-name: Reading File Namesread-event: Reading One Eventread-expression-history: Minibuffer Historyread-file-modes: Changing Filesread-file-name: Reading File Namesread-file-name-completion-ignore-case: Reading File Namesread-file-name-function: Reading File Namesread-from-minibuffer: Text from Minibufferread-from-string: Input Functionsread-input-method-name: Input Methodsread-kbd-macro: Describing Charactersread-key: Reading One Eventread-key-sequence: Key Sequence Inputread-key-sequence-vector: Key Sequence Inputread-minibuffer: Object from Minibufferread-no-blanks-input: Text from Minibufferread-non-nil-coding-system: User-Chosen Coding Systemsread-only (text property): Special Propertiesread-passwd: Reading a Passwordread-quoted-char: Quoted Character Inputread-quoted-char quitting: Quittingread-regexp: Text from Minibufferread-shell-command: Reading File Namesread-string: Text from Minibufferread-variable: High-Level Completionreal-last-command: Command Loop Inforecent-auto-save-p: Auto-Savingrecent-keys: Recording Inputrecenter: Textual Scrollingrecursion-depth: Recursive Editingrecursive-edit: Recursive Editingredirect-frame-focus: Input Focusredisplay: Forcing Redisplayredisplay-dont-pause: Forcing Redisplayredisplay-preemption-period: Forcing Redisplayredraw-display: Refresh Screenredraw-frame: Refresh Screenregexp-history: Minibuffer Historyregexp-opt: Regexp Functionsregexp-opt-depth: Regexp Functionsregexp-quote: Regexp Functionsregion-beginning: The Regionregion-end: The Regionregister-alist: Registersreindent-then-newline-and-indent: Mode-Specific Indentremhash: Hash Accessremove: Sets And Listsremove-from-invisibility-spec: Invisible Textremove-hook: Setting Hooksremove-images: Showing Imagesremove-list-of-text-properties: Changing Propertiesremove-overlays: Managing Overlaysremove-text-properties: Changing Propertiesremq: Sets And Listsrename-auto-save-file: Auto-Savingrename-buffer: Buffer Namesrename-file: Changing Filesreplace-buffer-in-windows: Displaying Buffersreplace-match: Replacing Matchreplace-re-search-function: Search and Replacereplace-regexp-in-string: Search and Replacereplace-search-function: Search and Replacerequire: Named Featuresrequire, customization keyword: Common Keywordsrequire-final-newline: Saving 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Idle Timerssafe, defcustom keyword: Variable Definitionssafe-length: List Elementssafe-local-eval-forms: File Local Variablessafe-local-variable-p: File Local Variablessafe-local-variable-values: File Local Variablessafe-magic (property): Magic File Namessame-window-buffer-names: Choosing Windowsame-window-p: Choosing Windowsame-window-regexps: Choosing Windowsave-abbrevs: Abbrev Filessave-buffer: Saving Bufferssave-buffer-coding-system: Encoding and I/Osave-current-buffer: Current Buffersave-excursion: Excursionssave-match-data: Saving Match Datasave-restriction: Narrowingsave-selected-window: Selecting Windowssave-some-buffers: Saving Bufferssave-window-excursion: Window Configurationsscalable-fonts-allowed: Font Selectionscan-lists: Motion via Parsingscan-sexps: Motion via Parsingscroll-bar-event-ratio: Accessing Scrollscroll-bar-mode: Scroll Barsscroll-bar-scale: Accessing Scrollscroll-bar-width: Scroll Barsscroll-conservatively: Textual Scrollingscroll-down: Textual Scrollingscroll-down-aggressively: Textual Scrollingscroll-left: Horizontal Scrollingscroll-margin: Textual Scrollingscroll-other-window: Textual Scrollingscroll-preserve-screen-position: Textual Scrollingscroll-right: Horizontal Scrollingscroll-step: Textual Scrollingscroll-up: Textual Scrollingscroll-up-aggressively: Textual Scrollingsearch-backward: String Searchsearch-failed: String Searchsearch-forward: String Searchsearch-map: Prefix Keyssearch-spaces-regexp: Regexp Searchseconds-to-time: Time Parsingselect-frame: Input Focusselect-frame-set-input-focus: Input Focusselect-safe-coding-system: User-Chosen Coding Systemsselect-safe-coding-system-accept-default-p: User-Chosen Coding Systemsselect-window: Selecting Windowsselected-frame: Input Focusselected-window: Selecting Windowsselection-coding-system: Window System Selectionsselective-display: Selective Displayselective-display-ellipses: Selective Displayself-insert-and-exit: Minibuffer Commandsself-insert-command: Commands for 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Char-Tablesset-char-table-parent: Char-Tablesset-char-table-range: Char-Tablesset-charset-priority: Character Setsset-coding-system-priority: Specifying Coding Systemsset-default: Default Valueset-default-file-modes: Changing Filesset-display-table-slot: Display Table Formatset-face-attribute: Attribute Functionsset-face-background: Attribute Functionsset-face-bold-p: Attribute Functionsset-face-font: Attribute Functionsset-face-foreground: Attribute Functionsset-face-inverse-video-p: Attribute Functionsset-face-italic-p: Attribute Functionsset-face-stipple: Attribute Functionsset-face-underline-p: Attribute Functionsset-file-modes: Changing Filesset-file-times: Changing Filesset-fontset-font: Fontsetsset-frame-configuration: Frame Configurationsset-frame-height: Size and Positionset-frame-parameter: Parameter Accessset-frame-position: Size and Positionset-frame-selected-window: Frames and Windowsset-frame-size: Size and Positionset-frame-width: Size and Positionset-fringe-bitmap-face: Customizing Bitmapsset-input-method: Input Methodsset-input-mode: Input Modesset-keyboard-coding-system: Terminal I/O Encodingset-keymap-parent: Inheritance and Keymapsset-left-margin: Marginsset-mark: The Markset-marker: Moving Markersset-marker-insertion-type: Marker Insertion Typesset-match-data: Entire Match Dataset-minibuffer-window: Minibuffer Windowsset-mouse-pixel-position: Mouse Positionset-mouse-position: Mouse Positionset-network-process-option: Network Optionsset-process-buffer: Process Buffersset-process-coding-system: Process Informationset-process-datagram-address: Datagramsset-process-filter: Filter Functionsset-process-plist: Process Informationset-process-query-on-exit-flag: Query Before Exitset-process-sentinel: Sentinelsset-register: Registersset-right-margin: Marginsset-screen-height: Size and Positionset-screen-width: Size and Positionset-standard-case-table: Case Tablesset-syntax-table: Syntax Table Functionsset-terminal-coding-system: Terminal I/O Encodingset-terminal-parameter: Terminal Parametersset-text-properties: Changing Propertiesset-time-zone-rule: Time of Dayset-visited-file-modtime: Modification Timeset-visited-file-name: Buffer File Nameset-window-buffer: Buffers and Windowsset-window-configuration: Window Configurationsset-window-dedicated-p: Dedicated Windowsset-window-display-table: Active Display Tableset-window-fringes: Fringe Size/Posset-window-hscroll: Horizontal Scrollingset-window-margins: Display Marginsset-window-parameter: Window Parametersset-window-point: Window Pointset-window-scroll-bars: Scroll Barsset-window-start: Window Start and Endset-window-vscroll: Vertical Scrollingsetcar: Setcarsetcdr: Setcdrsetenv: System Environmentsetplist: Symbol Plistssetq: Setting Variablessetq-default: Default Valuesetting-constant: Constant Variablesshell-command-history: Minibuffer Historyshell-command-to-string: Synchronous Processesshell-quote-argument: Shell Argumentsinteractive spec: Using Interactiveshow-help-function: Special Propertiesshrink-window: Resizing Windowsshrink-window-horizontally: Resizing Windowsshrink-window-if-larger-than-buffer: Resizing Windowssignal: Signaling Errorssignal-process: Signals to Processessigusr1 event: Misc Eventssigusr2 event: Misc Eventssin: Math Functionssingle-key-description: Describing Characterssit-for: Waitingsite-run-file: Init Fileskip-chars-backward: Skipping Charactersskip-chars-forward: Skipping Charactersskip-syntax-backward: Motion and Syntaxskip-syntax-forward: Motion and Syntaxsleep-for: Waitingsmall-temporary-file-directory: Unique File Namessmie-bnf->prec2: Operator Precedence Grammarssmie-close-block: SMIE setupsmie-down-list: SMIE setupsmie-merge-prec2s: Operator Precedence Grammarssmie-prec2->grammar: Operator Precedence Grammarssmie-precs->prec2: Operator Precedence Grammarssmie-rule-bolp: SMIE Indentation Helperssmie-rule-hanging-p: SMIE Indentation Helperssmie-rule-next-p: SMIE Indentation Helperssmie-rule-parent: SMIE Indentation Helperssmie-rule-parent-p: SMIE Indentation Helperssmie-rule-prev-p: SMIE Indentation Helperssmie-rule-separator: SMIE Indentation Helperssmie-rule-sibling-p: SMIE Indentation Helperssmie-setup: SMIE setupSnarf-documentation: Accessing Documentationsort: Rearrangementsort-columns: Sortingsort-fields: Sortingsort-fold-case: Sortingsort-lines: Sortingsort-numeric-base: Sortingsort-numeric-fields: Sortingsort-pages: Sortingsort-paragraphs: Sortingsort-regexp-fields: Sortingsort-subr: Sortingspecial: Major Mode Conventionsspecial-display-buffer-names: Choosing Windowspecial-display-frame-alist: Choosing Windowspecial-display-function: Choosing Windowspecial-display-p: Choosing Windowspecial-display-popup-frame: Choosing Windowspecial-display-regexps: Choosing Windowspecial-event-map: Controlling Active Mapssplit-height-threshold: Choosing Windowsplit-string: Creating Stringssplit-string-and-unquote: Shell Argumentssplit-string-default-separators: Creating Stringssplit-width-threshold: Choosing Windowsplit-window: Splitting Windowssplit-window-horizontally: Splitting Windowssplit-window-keep-point: Splitting Windowssplit-window-preferred-function: Choosing Windowsplit-window-sensibly: Choosing Windowsplit-window-vertically: Splitting Windowssqrt: Math Functionsstandard-case-table: Case Tablesstandard-category-table: Categoriesstandard-display-table: Active Display Tablestandard-input: Input Functionsstandard-output: Output Variablesstandard-syntax-table: Standard Syntax Tablesstandard-translation-table-for-decode: Translation of Charactersstandard-translation-table-for-encode: Translation of Charactersstart-file-process: Asynchronous Processesstart-file-process-shell-command: Asynchronous Processesstart-process: Asynchronous Processesstart-process, command-line arguments from minibuffer: Shell Argumentsstart-process-shell-command: Asynchronous Processesstaticpro, protection from GC: Writing Emacs Primitivesstop-process: Signals to Processesstore-match-data: Entire Match Datastore-substring: Modifying Stringsstring: Creating Stringsstring quote: Syntax Class Tablestring-as-multibyte: Selecting a Representationstring-as-unibyte: Selecting a Representationstring-bytes: Text Representationsstring-chars-consed: Memory Usagestring-equal: Text Comparisonstring-lessp: Text Comparisonstring-match: Regexp Searchstring-match-p: Regexp Searchstring-or-null-p: Predicates for Stringsstring-to-char: String Conversionstring-to-int: String Conversionstring-to-multibyte: Converting Representationsstring-to-number: String Conversionstring-to-syntax: Syntax Table Internalsstring-to-unibyte: Converting Representationsstring-width: Widthstring<: Text Comparisonstring=: Text Comparisonstringp: Predicates for Stringsstrings-consed: Memory Usagesubr-arity: What Is a Functionsubrp: What Is a Functionsubst-char-in-region: Substitutionsubstitute-command-keys: Keys in Documentationsubstitute-in-file-name: File Name Expansionsubstitute-key-definition: Changing Key Bindingssubstring: Creating Stringssubstring-no-properties: Creating Stringssuppress-keymap: Changing Key Bindingsno-redraw-on-reenter): Refresh Screensuspend-emacs: Suspending Emacssuspend-frame: Suspending Emacssuspend-hook: Suspending Emacssuspend-resume-hook: Suspending Emacssuspend-tty: Suspending Emacssuspend-tty-functions: Suspending Emacsswitch-to-buffer: Displaying Buffersswitch-to-buffer-other-window: Displaying Bufferssxhash: Defining Hashsymbol constituent: Syntax Class Tablesymbol-file: Where Definedsymbol-function: Function Cellssymbol-name: Creating Symbolssymbol-plist: Symbol Plistssymbol-value: Accessing Variablessymbolp: Symbolssymbols-consed: Memory Usagesyntax-after: Syntax Table Internalssyntax-begin-function: Position Parsesyntax-class: Syntax Table Internalssyntax-ppss: Position Parsesyntax-ppss-flush-cache: Position Parsesyntax-ppss-toplevel-pos: Parser Statesyntax-table: Syntax Table Functionssyntax-table (text property): Syntax Propertiessyntax-table-p: Syntax Basicssystem-configuration: System Environmentsystem-key-alist: X11 Keysymssystem-messages-locale: Localessystem-name: System Environmentsystem-time-locale: Localessystem-type: System Environmentt: nil和tt input stream: Input Streamst output stream: Output Streamstab-stop-list: Indent Tabstab-to-tab-stop: Indent Tabstab-width: Usual Displaytag, customization keyword: Common Keywordstan: Math Functionstemacs: Building EmacsTEMP environment variable: Unique File Namestemp-buffer-setup-hook: Temporary Displaystemp-buffer-show-function: Temporary Displaystemp-buffer-show-hook: Temporary Displaystemporary-file-directory: Unique File NamesTERM environment variable: Terminal-Specificterm-file-prefix: Terminal-Specificterm-setup-hook: Terminal-Specificterminal-coding-system: Terminal I/O Encodingterminal-list: Multiple Terminalsterminal-live-p: Framesterminal-name: Multiple Terminalsterminal-parameter: Terminal Parametersterminal-parameters: Terminal Parametersterpri: Output Functionstest-completion: Basic Completiontestcover-mark-all: Test Coveragetestcover-next-mark: Test Coveragetestcover-start: Test Coveragetext-char-description: Describing Characterstext-mode-abbrev-table: Standard Abbrev Tablestext-mode-map: Standard Keymapstext-mode-syntax-table: Standard Syntax Tablestext-properties-at: Examining Propertiestext-property-any: Property Searchtext-property-default-nonsticky: Sticky Propertiestext-property-not-all: Property Searchthing-at-point: Buffer Contentsthis-command: Command Loop Infothis-command-keys: Command Loop Infothis-command-keys-shift-translated: Key Sequence Inputthis-command-keys-vector: Command Loop Infothis-original-command: Command Loop Infothree-step-help: Help Functionsthrow: Catch and Throwthrow example: Recursive Editingtime-add: Time Calculationstime-less-p: Time Calculationstime-subtract: Time Calculationstime-to-day-in-year: Time Calculationstime-to-days: Time Calculationstimer-max-repeats: TimersTMP environment variable: Unique File NamesTMPDIR environment variable: Unique File Namestoggle-read-only: Read Only Bufferstool-bar-add-item: Tool Bartool-bar-add-item-from-menu: Tool Bartool-bar-border: Tool Bartool-bar-button-margin: Tool Bartool-bar-button-relief: Tool Bartool-bar-local-item-from-menu: Tool Bartool-bar-map: Tool Bartop-level: Recursive Editingtq-close: Transaction Queuestq-create: Transaction Queuestq-enqueue: Transaction Queuestrack-mouse: Mouse Trackingtransient-mark-mode: The Marktranslate-region: Substitutiontranslation-table-for-input: Translation of Characterstranspose-regions: Transpositiontruncate: Numeric Conversionstruncate-lines: Truncationtruncate-partial-width-windows: Truncationtruncate-string-to-width: Widthtry-completion: Basic Completiontty-color-alist: Text Terminal Colorstty-color-approximate: Text Terminal Colorstty-color-clear: Text Terminal Colorstty-color-define: Text Terminal Colorstty-color-translate: Text Terminal Colorstty-erase-char: System Environmenttype (button property): Button Propertiestype, defcustom keyword: Customization Typestype-of: 类型判定unbury-buffer: The Buffer Listundecided coding-system, when encoding: Explicit Encodingundefined: Functions for Key Lookupundefined in keymap: Key Lookupunderline-minimum-offset: Face Attributesundo-ask-before-discard: Maintaining Undoundo-boundary: Undoundo-in-progress: Undoundo-limit: Maintaining Undoundo-outer-limit: Maintaining Undoundo-strong-limit: Maintaining Undounhandled-file-name-directory: Magic File Namesunibyte-char-to-multibyte: Converting Representationsunibyte-string: Text Representationsunicode, a charset: Character Setsunintern: Creating Symbolsuniversal-argument: Prefix Command Argumentsunless: Conditionalsunload-feature: Unloadingunload-feature-special-hooks: Unloadingunlock-buffer: File Locksunread-command-char: Event Input Miscunread-command-events: Event Input Miscunsafep: Function Safetyunwind-protect: Cleanupsup-list: List Motionupcase: Case Conversionupcase-initials: Case Conversionupcase-region: Case Changesupcase-word: Case Changesupdate-directory-autoloads: Autoloadupdate-file-autoloads: Autoloaduse-global-map: Controlling Active Mapsuse-hard-newlines: Fillinguse-local-map: Controlling Active Mapsuse-region-p: The Regionuser-emacs-directory: Init Fileuser-full-name: User Identificationuser-init-file: Init Fileuser-login-name: User Identificationuser-mail-address: User Identificationuser-real-login-name: User Identificationuser-real-uid: User Identificationuser-uid: User Identificationuser-variable-p: Defining Variablesuser-variable-p example: High-Level Completionutf-8-emacs coding system: Coding System Basicsvalues: Evalvariable-documentation: Documentation Basicsvariable-interactive: Defining Variablesvc-mode: Mode Line Variablesvc-prefix-map: Prefix Keysvconcat: Vector Functionsvector: Vector Functionsvector-cells-consed: Memory Usagevectorp: Vector Functionsverify-visited-file-modtime: Modification Timeversion, customization keyword: Common Keywordsversion-control: Numbered Backupsvertical-line prefix key: Key Sequence Inputvertical-motion: Screen Linesvertical-scroll-bar: Scroll Barsvertical-scroll-bar prefix key: Key Sequence Inputview-file: Visiting Functionsview-mode-map: Standard Keymapsview-register: Registersvisible-bell: Beepingvisible-frame-list: Finding All Framesvisited-file-modtime: Modification Timevoid-function: Function Cellsvoid-text-area-pointer: Pointer Shapevoid-variable: Void Variableswaiting-for-user-input-p: Sentinelswalk-windows: Cyclic Window Orderingwarn: Warning Basicswarning-fill-prefix: Warning Variableswarning-levels: Warning Variableswarning-minimum-level: Warning Optionswarning-minimum-log-level: Warning Optionswarning-prefix-function: Warning Variableswarning-series: Warning Variableswarning-suppress-log-types: Warning Optionswarning-suppress-types: Warning Optionswarning-type-format: Warning Variableswheel-down event: Misc Eventswheel-up event: Misc Eventswhen: Conditionalswhere-is-internal: Scanning Keymapswhile: Iterationwhile-no-input: Event Input Miscwhitespace character: Syntax Class Tablewholenump: Predicates on Numberswiden: Narrowingwindow (overlay property): Overlay Propertieswindow-at: Coordinates and Windowswindow-body-height: Size of Windowwindow-buffer: Buffers and Windowswindow-configuration-change-hook: Window Hookswindow-configuration-frame: Window Configurationswindow-configuration-p: Window Configurationswindow-current-scroll-bars: Scroll Barswindow-dedicated-p: Dedicated Windowswindow-display-table: Active Display Tablewindow-edges: Size of Windowwindow-end: Window Start and Endwindow-frame: Frames and Windowswindow-fringes: Fringe Size/Poswindow-full-height-p: Size of Windowwindow-full-width-p: Size of Windowwindow-height: Size of Windowwindow-hscroll: Horizontal Scrollingwindow-inside-edges: Size of Windowwindow-inside-pixel-edges: Size of Windowwindow-line-height: Window Start and Endwindow-list: Cyclic Window Orderingwindow-live-p: Deleting Windowswindow-margins: Display Marginswindow-min-height: Resizing Windowswindow-min-width: Resizing Windowswindow-minibuffer-p: Minibuffer Windowswindow-parameter: Window Parameterswindow-parameters: Window Parameterswindow-pixel-edges: Size of Windowwindow-point: Window Pointwindow-point-insertion-type: Window Pointwindow-scroll-bars: Scroll Barswindow-scroll-functions: Window Hookswindow-setup-hook: Window Systemswindow-size-change-functions: Window Hookswindow-size-fixed: Resizing Windowswindow-start: Window Start and Endwindow-system: Window Systemswindow-system-initialization-alist: Startup Summarywindow-tree: Window Treewindow-vscroll: Vertical Scrollingwindow-width: Size of Windowwindowp: Basic Windowswith-case-table: Case Tableswith-coding-priority: Specifying Coding Systemswith-current-buffer: Current Bufferwith-help-window: Help Functionswith-local-quit: Quittingwith-no-warnings: Compiler Errorswith-output-to-string: Output Functionswith-output-to-temp-buffer: Temporary Displayswith-selected-window: Selecting Windowswith-syntax-table: Syntax Table Functionswith-temp-buffer: Current Bufferwith-temp-file: Writing to Fileswith-temp-message: Displaying Messageswith-timeout: Timersword constituent: Syntax Class Tableword-search-backward: String Searchword-search-backward-lax: String Searchword-search-forward: String Searchword-search-forward-lax: String Searchwords-include-escapes: Word Motionwrap-prefix: Truncationwrite-abbrev-file: Abbrev Fileswrite-char: Output Functionswrite-contents-functions: Saving Bufferswrite-file: Saving Bufferswrite-file-functions: Saving Bufferswrite-region: Writing to Fileswrite-region-annotate-functions: Format Conversion Piecemealwrite-region-post-annotation-function: Format Conversion Piecemealwrong-number-of-arguments: Argument Listx-alt-keysym: X11 Keysymsx-bitmap-file-path: Face Attributesx-close-connection: Multiple Terminalsx-color-defined-p: Color Namesx-color-values: Color Namesx-defined-colors: Color Namesx-display-color-p: Display Feature Testingx-display-list: Multiple Terminalsx-dnd-known-types: Drag and Dropx-dnd-test-function: Drag and Dropx-dnd-types-alist: Drag and Dropx-family-fonts: Font Lookupx-get-cut-buffer: Window System Selectionsx-get-resource: Resourcesx-get-selection: Window System Selectionsx-hyper-keysym: X11 Keysymsx-list-fonts: Font Lookupx-meta-keysym: X11 Keysymsx-open-connection: Multiple Terminalsx-parse-geometry: Geometryx-pointer-shape: Pointer Shapex-popup-dialog: Dialog Boxesx-popup-menu: Pop-Up Menusx-resource-class: Resourcesx-resource-name: Resourcesx-select-enable-clipboard: Window System Selectionsx-sensitive-text-pointer-shape: Pointer Shapex-server-vendor: Display Feature Testingx-server-version: Display Feature Testingx-set-cut-buffer: Window System Selectionsx-set-selection: Window System Selectionsx-super-keysym: X11 Keysymsy-or-n-p: Yes-or-No Queriesy-or-n-p-with-timeout: Yes-or-No Queriesyank: Yank Commandsyank-pop: Yank Commandsyank-undo-function: Yank Commandsyes-or-no-p: Yes-or-No Querieszerop: Predicates on Numbersnil: 盒子图解无效读取语法: 打印表示错误类型的参数: 类型判定[1] There is no strictly equivalent way to add an element to
the end of a list. You can use (append listname (list
newelt)), which creates a whole new list by copying listname
and adding newelt to its end. Or you can use (nconc
listname (list newelt)), which modifies listname
by following all the cdrs and then replacing the terminating
nil. Compare this to adding an element to the beginning of a
list with cons, which neither copies nor modifies the list.
[2] This usage of “key” is not related to the term “key sequence”; it means a value used to look up an item in a table. In this case, the table is the alist, and the alist associations are the items.
[3] This definition of “environment” is specifically not intended to include all the data that can affect the result of a program.
[4]
Actually, you should use ignore-errors in such a simple case;
see below.
[5] They may also be declared equivalently in cus-start.el.
[6] The MS-DOS version of Emacs uses _dir-locals.el instead, due to limitations of the DOS filesystems.
[7] This is related to, but different from currying, which transforms a function that takes multiple arguments in such a way that it can be called as a chain of functions, each one with a single argument.
[8] Some elements actually supply two parameters.
[9] Button-down is the conservative antithesis of drag.
[10] It is required for menus which do not use a toolkit, e.g. under MS-DOS.
[11] In this case, the text is first
encoded using the utf-8 coding system and then rendered by the
toolkit as it sees fit.
[12] An RFC, an acronym for Request for Comments, is a numbered Internet informational document describing a standard. RFCs are usually written by technical experts acting on their own initiative, and are traditionally written in a pragmatic, experience-driven manner.
[13] For an explanation of what is an RFC, see the footnote in Base 64.
[14] This internal representation is based on one of the encodings defined by the Unicode Standard, called UTF-8, for representing any Unicode codepoint, but Emacs extends UTF-8 to represent the additional codepoints it uses for raw 8-bit bytes and characters not unified with Unicode.
[15] Note that the Unicode spec writes these tag names inside ‘<..>’ brackets. The tag names in Emacs do not include the brackets; e.g., Unicode specifies ‘<small>’ where Emacs uses ‘small’.
[16] On other systems, Emacs uses a Lisp emulation of
ls; see Contents of Directories.
[17] In this context, the term font has nothing to do with Font Lock (see Font Lock Mode).
[18] The benefits of a Common Lisp-style package system are considered not to outweigh the costs.
[19] Formerly, strings were a special
exception; in older Emacs versions, every local variable that might
point to a string needed a GCPRO.